What is a one-sentence summary of the following article?
No matter whether you sleep on your back, stomach, or side, adding pillows can help provide support. Basically, you want to add a pillow anywhere there's a space between your body and the mattress.  For instance, if you sleep on your stomach, which is the worst position for your back and posture, place a flat pillow under your stomach to provide support. Choose a flat pillow or no pillow for your head. If you sleep on your back, place a small pillow behind your knees, and choose a supportive pillow for your head. If you sleep on your side, place a pillow between your knees and pull them up towards your chest. Pick a pillow for your head that keeps your spine straight, or use a full body pillow. Avoid turning at your waist while you are in bed. Instead, keep your back straight and your stomach muscles tight, and turn your whole body when you want to reposition yourself. While you may have heard that one mattress or another is best for a healthy back, the truth is whatever works for you is best. Choose one that lets you rest comfortably and wake up pain free.  Remember to replace your mattress every decade or so. If your mattress isn't providing the support you need, add a board between the box springs and mattress, which should keep it from sagging.

Summary:
Provide support for your back with pillows while sleeping. Turn your body as 1 unit when laying down. Sleep with good posture by choosing a comfortable mattress.