When a mattress is too firm, it does not allow the shoulder to sink in appropriately, creating concentrated pressure on the shoulder joint. This pressure can build up overnight and result in pain, numbness, or stiffness by morning. A mattress with adequate cushioning in the comfort layer helps the shoulder settle in while keeping the spine properly aligned. Choosing a medium-soft or plush mattress is often the most effective way to reduce shoulder pain for side sleepers.
