NBC: Here is what you should know about mattress firmness and sleep health.

Why does how you sleep decide how firm your mattress should be? Well, depending on your usual sleep position, you need different things from your mattress to keep your spine properly aligned — spinal alignment is the crucial thing here, I’ve learned in my time as a sleep writer. For example, side sleepers need their shoulders and hips to sink further into the mattress to achieve spinal alignment, whereas back and stomach sleepers need to sink less — otherwise their spine will arch. Side sleepers also can experience significant pressure on their shoulders and hips if their mattress is too firm, since those parts of their body tend to sink deeply into the mattress. That’s less of an issue for back and stomach sleepers.

Heavier people (over 230 pounds, according to Logan Foley, managing editor at Sleep Foundation, in our guide to firm mattresses) sink further into any mattress, and heavier side sleepers might sink too far into a very soft mattress. But lighter back sleepers might feel like they’re sleeping on cement with a firm mattress, so it’s a sliding scale. But in general, heavier people might benefit from firmer mattresses than lighter people who use the same sleep position.

Comfort is subjective, though, and not always predictable — two people of the same body type, height and weight might have wildly different mattress preferences. Even if it’s largely a matter of personal taste, comfort can be directly related to sleep health. According to Dr. Seema Khosla, medical director of the North Dakota Center for Sleep, if you experience pain or discomfort while you sleep, your sleep can be more fragmented as a result.

“Sometimes you’re just hanging out in lighter sleep instead of deeper sleep,” Khosla said.

Get the full story at nbc.com.