As a chiropractor and mattress designer, I understand the importance of spinal alignment, especially during sleep. Proper spinal alignment during sleep can prevent undue stress and strain on the spine, which can lead to back pain and discomfort. Back pain has been identified as one of the possible causes of inappropriate sleep in adults, according to pubmed.ncbi.nlm.nih.gov. Poor spinal alignment may also lead to poor sleep quality, which can result in fatigue, irritability, and other health problems.
Importance of spinal alignment
Spinal alignment is an essential aspect of sleep that has been subject to research in recent times. The alignment of the spine during sleep is crucial for ensuring that the spine is not subjected to undue stress and strain, which can result in back pain and discomfort.
Spinal alignment refers to the position of the spine when standing, sitting, or lying down. Good spinal alignment is important for maintaining good health and preventing pain and discomfort. The spine is made up of 33 vertebrae that are stacked on top of each other and separated by discs that act as shock absorbers. Each vertebra is connected to the one above and below it by facet joints, which allow for movement in the spine. 
Sleep is also an important factor when it comes to spinal alignment. Poor sleep posture can cause or aggravate back pain. The best position for sleeping is on your back, as it allows the spine to rest in a neutral position. Sleeping on your stomach is not recommended as it causes the neck and spine to be out of alignment. Sleeping on your side is okay, but it is important to use a pillow between your knees to maintain proper spinal alignment. 
Effects on sleep quality and health
According to pubmed.ncbi.nlm.nih.gov, back pain has been identified as one of the possible causes of inappropriate sleep in adults. Poor spinal alignment may also lead to poor sleep quality, which can result in fatigue, irritability, and other health problems.
Mattresses and spinal alignment
There is no consensus on the type of mattress that is best for promoting spinal alignment and sleep quality, as the literature on the topic is quite extensive. A systematic review of controlled trials published since 2000 found that a medium-firm mattress that is custom inflated (self-adjusted) is optimal for promoting sleep comfort, quality, and spinal alignment . This is consistent with my recommendation that a medium-firm to firm mattress is best for back sleepers.
Latex foam mattresses
As a chiropractor and mattress designer, my favorite material to create mattresses with is natural latex foam. However, it is also the hardest to design due to its high responsiveness, so it took trials and data collection to design the optimum mattress for support and comfort. In general, the literature suggests that the type of mattress and pillow material can affect spinal alignment during sleep.
Temperature and mattress firmness
The literature is not yet sufficient to determine the appropriate temperature of the optimum mattress. However, it is essential to consider individual preferences and external factors, such as room temperature and humidity, when selecting a mattress with the right firmness and temperature.
A systematic review and meta-analysis of pillow designs found that appropriate pillow design can have a positive effect on neck pain, waking symptoms, neck disability, sleep quality, and spinal alignment in adults . The study found that pillows that provide adequate neck support are best for promoting spinal alignment and reducing neck pain.
According to my experience, the pillow should support the neck in a neutral position, with the chin neither tilting back nor being pushed towards the chest. It is also important to avoid having both the neck and shoulders on the pillow, as this can result in spinal misalignment.
Latex pillow material
Based on my research, there is moderate evidence that a latex pillow material can improve sleep comfort and quality, decrease neck pain, and improve overall function . The study evaluated the level of evidence of different pillow parameters to promote and enhance sleep quality, spinal alignment, and decrease waking symptoms. Researchers concluded that a latex pillow material has the greatest evidence in improving sleep comfort and quality, decreasing neck pain, and promoting optimal spinal alignment.
Contoured pillow design
I have found that a contoured pillow design with higher sides to accommodate side sleepers and a lower, flattened middle to accommodate back sleepers, and a pillow height between 7 and 11 centimetres can improve sleep quality, spinal alignment, and decrease sleep-related neck pain.
According to my experience, back sleeping is usually considered the best sleep position when it comes to proper alignment. To optimise sleep posture on the back, it is recommended to use a mattress that is medium-firm to firm but still allows the buttocks to moderately sink into the mattress. Leg positioning should also be considered, and the legs should be kept in a straight line without spreading them wide or twisting them in either direction. A small pillow underneath the knees can reduce lower-back strain. Some people will find that a pillow beneath the lumbar region of the spine is beneficial, particularly on a firm mattress .
Side sleeping can also promote proper spinal alignment if the right pillow and mattress are used. A contoured pillow design with higher sides can provide adequate support for the neck and head, while a medium-firm mattress can help maintain the natural curve of the spine. It is also helpful to place a pillow between the knees to prevent the upper leg from pulling the spine out of alignment.
Stomach sleeping is generally not recommended, as it can cause strain on the neck and spine. However, if this is the only comfortable position, using a thin pillow or no pillow at all can help reduce the stress on the neck. Placing a pillow under the pelvis can also provide additional support and help maintain the natural curve of the spine.
Leg and lumbar positioning
Proper leg and lumbar positioning during sleep can contribute to better spinal alignment. Keeping the legs in a straight line and avoiding excessive twisting can help prevent strain on the spine. Additionally, using pillows to support the lumbar region or under the knees can further improve alignment and reduce discomfort.
Strategies for improving spinal alignment
Choose a mattress that provides adequate support and comfort. A medium-firm to firm mattress, particularly one made from natural latex foam, is often recommended for back sleepers.
Select a pillow that offers proper neck support and is made from a material with evidence-based benefits, such as latex. Contoured pillow designs can accommodate different sleep positions and contribute to better spinal alignment.
Ensure that your sleep environment is conducive to restful sleep by maintaining an appropriate room temperature, reducing noise, and minimizing exposure to light.
My experience as a chiropractor and mattress designer
From my professional perspective, natural latex foam is a favored material for designing mattresses due to its unique properties that offer both support and comfort. However, designing the ideal mattress with latex foam can be challenging because of its high responsiveness. With extensive research and testing, it is possible to create a mattress that promotes optimal spinal alignment and sleep quality.
In summary, as a chiropractor and mattress designer, I believe that proper spinal alignment is crucial for sleep quality and overall health. A combination of the right mattress, pillow design, and sleep position can help ensure optimal spinal alignment during sleep. Medium-firm mattresses, particularly those made from natural latex foam, can provide excellent support and comfort for back sleepers. Contoured pillow designs made from latex material can also enhance sleep quality and spinal alignment, especially for side sleepers. Overall, understanding and addressing the factors that affect spinal alignment during sleep can lead to improved sleep quality, reduced back pain, and better overall health.