A mattress must support your body in two ways. It must be fi-rm enough to keep your spine horizontal. Your body must not sag as if in a hammock. It must follow your curves. This is called good conformity. Test for conformity by lying on your side-the mattress should come up strongly into the waist area. To meet the first requirement, modern mattresses have firm springs, and some have extra support in the middle area. To meet the second, a large number of smaller springs is helpful.
Your weight and your shape affect your choice of mattress. A heavy person needs heavy springs-more firmness. Others need
less firmness so that hips will sink in a little. If your hips are much wider than your waist; you will need lots of conformity so that waist and lumbar spine are supported. Be sure to try out mattresses in the showroom before you buy. Take your time.
A modern foundation gives a strong, flat support to the mattress. When the foundation sags and you can’t afford a new one, a bed board should help. Use 3/4 inch plywood between the mattress and the foundation. A piece 4 feet wide by 5 feet long ( easily cut at a lumber yard) is usually large enough for a double or queen size bed. A king size bed (76 inches wide) requires two 3 feet by 5 feet pieces. Bear in mind that a bed board will not fix a poor mattress.
Waterbeds, some people say, are helpful for their backs; others say their backs are worse. Newer models have extra support in the lumbar area. Try one at least overnight before you buy.
Sleeping position. On your side is best. Put arms in front and partially curl your body. A pillow should fit the space between mattress and head. Head should stay in line with body, tilted neither up nor down. Foam pillows tend to hold head too high.
Sleeping on your back is okay if your knees are raised and supported. A blanket roll or large pillows can be used temporarily, but adjustable beds (either rented or purchased) are easier. For your head, use no pillow or a very thin one.
Sleeping on your stomach strains the back. If that is your only comfortable position, try a thin pillow under your pelvis.