Use a firm mattress. Placing a board between the mattress and box spring can provide a temporary fix for one that is sagging.Lie on your back or side. When lying on the side, a pillow between the knees helps maintain a neutral spine.Use a cervical roll (a foam roll approximately 3 inches in diameter and 18 inches long) to support the natural curves in your neck or low back. BACK.COM
Buy good bedding
A firm mattress supports the spine and helps maintain the same shape as someone with upright posture.
There's no one-size-fits-all approach when it comes to buying a mattress. Look for a mattress that comfortably supports your shoulders, hips and lower back. If the mattress is too soft, you might wake up with a backache. If the mattress is too firm, uncomfortable pressure might leave you tossing and turning all night. Don't rely on the advertised level of firmness, which may vary from brand to brand. Instead, spend plenty of time lying on display mattresses to get a feel for what's comfortable. Keep in mind that you and your bed partner might have different preferences about mattress firmness. If you can't agree on what's comfortable, you might consider an adjustable mattress that allows you to set one side of the mattress softer or firmer than the other.KENNETH BERGE M.D. MAYO CLINIC
As you can see these two sources agree on a good supporting mattress but not on the hardness. Unfortunately there are other good arguments for a soft mattress to help with other ailments. The one common factor in 90% of the articles other than the firmness is that too soft isn't good. A mattress with a lot of upholstery tends to have deeper impressions causing the back to be out of line and aggravating any damage that already exists or trains the body to be out of lineKeep this in mind while shopping the reason a salesperson wants to sell you a softer mattress is that there are more choices at higher dollars meaning more profit or commission. Hard mattresses get softer and soft mattresses get lumpier as time goes on.
You will find terms and conditions on Mattress Information home page