You spend about a third of every day in bed. Whether that time is spent blissfully slumbering -- or tossing and turning -- depends a lot on your mattress. "A mattress can impact a person's sleep," says Michael Decker, PhD, RN, associate professor at Georgia State University and spokesman for the American Academy of Sleep Medicine. One way that your mattress affects your sleep has to do with the network of fine blood vessels, called capillaries, that runs underneath your skin. "When you lie on any part of your body for an extended period of time, the weight of it reduces the flow of blood through those blood vessels, which deprives the skin of oxygen and nutrients," Decker says. This causes nerve cells and pain sensors in your skin to send a message to your brain for you to roll over. Rolling over restores blood flow to the area, but it also briefly interrupts your sleep. Ideally, a mattress that reduces the pressure points on your body should give you a better night's sleep, Decker says. Yet the ideal mattress is different for each person. Which Mattress Is Right for You? Finding the right mattress isn't about searching out the highest-tech brand or spending the most money. "A much more expensive mattress doesn't necessarily mean it's better," Decker says. A high price tag is a product of both the materials that go into the mattress, and the marketing that helps sell it. Instead of focusing on price and brand name, think about what you want in a mattress. "Selecting a mattress is very personal," Decker says. Some people prefer a firmer mattress; others favor a softer style. Although there isn't a lot of scientific evidence to prove that one type of mattress will help you sleep better than another, people with certain medical conditions do seem to rest easier on a particular mattress style. Anyone with back or neck pain should take a Goldilocks approach to mattress buying: not too hard, and not too soft. "If you're on too soft [of] a mattress, you'll start to sink down to the bottom. But on too hard of a mattress you have too much pressure on the sacrum, and on the shoulders, and on the back of the head," says Howard Levy, MD, an Emory University assistant professor of orthopaedics, physical medicine, and rehabilitation. A medium-firm mattress, or a firm mattress with a softer pillow top, will give your spine that "just-right" balance of support and cushioning. An adjustable bed can be a good buy if you need to sleep with your head raised. Doctors sometimes recommend elevating the head to help people with COPD breathe easier, or to prevent nighttime heartburn from GERD. These beds can also allow you to adjust your knees and hips to a 90-degree angle, relieving some of the pressure on sore joints, Levy says. If you have allergies or asthma, you might have considered buying a bed labeled "hypoallergenic." "There are a lot of claims made by mattress manufacturers that their mattresses are hypoallergenic or don't support the growth of dust mites, but I don't know of scientific evidence to support these claims," says Paul V. Williams, MD, a pediatrics professor at the University of Washington School of Medicine and an allergist at Northwest Allergy and Asthma Center in Washington state. Williams says dust mites will live anywhere there's food -- and that food is your dead skin cells. Instead of investing in an allergy-free mattress, slip on a washable mattress encasing. It will form a barrier that prevents dust mites from getting to you. A mattress encasing cuts allergen growth by robbing dust mites of their food supply, Williams says. And what about those space-age memory foam mattresses, which can cost thousands of dollars? There is some evidence they can help with back problems and improve sleep, but their advantage over a regular coil mattress is only slight. Where memory foam mattresses can really help you sleep is if you have an active bed partner who is keeping you awake, Decker says. Foam mattresses reduce motion transfer, letting you lie still while your partner tosses and turns. Test Drive a Mattress Before You Buy "You wouldn't buy a car without test driving it," Decker says. So why would you invest hundreds -- or even thousands of dollars in a mattress without trying it out first? Take any new mattress you're considering for a test nap. "People should not be embarrassed to go into a store and lay on a mattress for 20 minutes," Decker says. For a more realistic test, sleep in the beds at different hotel chains when you travel. If you get an especially good night's sleep on one of them, ask the desk clerk what brand it is. When you test out a mattress, make sure it feels comfortable in every position, especially the side you favor for sleeping. The mattress should be supportive where you need it, without putting too much pressure on your body, Levy says. Time for a New Mattress If you've been having trouble sleeping, the problem might not be your mattress type, but its age. "It's really important for people to realize that mattresses have a certain lifespan," Decker says. Keep your mattress too long, and the foam and other materials inside it will start to break down, compromising its ability to support your body. Decker recommends keeping your mattress for no more than 10 years. After that, it's time to go mattress shopping again.