The right mattress for you will provide your body with enough support to keep your spine in proper alignment while you sleep, and enough cushioning to relieve pressure under sensitive pressure points like the shoulders and hips.
The first thing that your mattress must do is support your spine in neutral alignment. This means that the shape of your spine when you are lying down should be the same as when you're standing up straight. Your spine should maintain its natural “S” curve when you are on your belly or your back, and it should be straight when you’re on your side. Ask a friend to look at your back when you're testing mattresses in the store. If there are gaps between your body and the mattress, that means you need more support from your mattress in those areas.
The term "support" refers to the aspects of the bed that push back in order to hold your spine in position while you sleep. Unlike comfort, which is largely a matter of personal preference, everyone requires support from their mattress. Improper or inadequate support can cause tension or back pain as your muscles compensate by working to keep your spine in alignment. Though mattress companies use words like "firm" or "extra firm" to explain the support provided by a bed, what they are really describing is the extent to which the inner core of the mattress (what you feel when you put one knee on the bed and then lean your weight into it) is "springy" or "stiff." The amount of support your body needs depends on your sleep position and your size. Different combinations of mattress types and materials can work for different bodies; the best way to find a mattress that provides proper support is to test out a number of different mattresses in the store.
Imagine there is a pressure map underneath your body when you’re lying on a bed. It would look like a heat map—places where the pressure per square inch is highest would be orange and red (these are known as “pressure points”), and places where there’s less pressure would be blue and green. Pressure relief means that the mattress gives enough to relieve pressure under weight-bearing pressure points like the hips and shoulders, and that it rises to meet the parts of your body that don’t stick out as much, like the small of your back.
Inadequate pressure relief is a principal cause of tossing and turning in the night, since your body unconsciously adjusts when you feel pain or pressure in certain areas, or when part of your body loses circulation due to inadequate pressure relief. The more contact your body has with the bed, the more evenly your body’s weight will be distributed over the surface of the bed, and the less pressure you’ll experience throughout the night.
A mattress’ ability to provide pressure relief takes a little time to assess. As opposed to the general comfort of the mattress, which is really about personal preference and can be assessed quickly, pressure relief has a more scientific, measurable quality. Practically speaking, it can take at least 10 minutes before you notice the signs that a mattress is not providing adequate pressure relief for you. You might notice, for example, that the mattress feels uncomfortable under your shoulder, or that your arm is slowly falling asleep.
Pressure relief can sometimes run in conflict to support. A mattress with a slight hammocking effect, for example, may be just what your body needs for maximum pressure relief, but it is unlikely to support your spine in proper alignment. The right mattress for you provides a balance of both.