The National Sleep Foundation says a good mattress lasts 9 to 10 years. Another study finds that most people who buy a new bed every five years sleep better and have less back pain.

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We all know we should get more sleep. What we might not know is that our old pillows and mattresses could be contributing to the quality of our slumber.

Here’s a little primer for those shopping for a new sleep surface.

How to make sense of mattress sales

Gradual changes over time cause mattresses to become less comfortable and less supportive. The National Sleep Foundation says a good mattress lasts 9 to 10 years, but a recent study by Oklahoma State University showed that most people who buy a new bed every five years sleep better and experience less back pain.

Consumer Reports recommends buying a new mattress “if you wake up tired or achy, you tend to sleep better at hotels than at home, your mattress looks saggy or lumpy, you’re over age 40, or your mattress is five to seven years old.”

The product-review magazine says it receives more questions about mattresses than any other product aside from cars, and it doesn’t rate mattresses by brand because of the way they are marketed.

Says the report: “Manufacturers usually modify innerspring mattresses for different sellers, changing the color, padding, quilting pattern, and so forth. Then each seller can call the mattress by a different name. Consumers are the losers.”

Both Sealy and Simmons mattress companies have buying guides for consumers on their Web sites that explain differences in their products.

What to consider when buying a mattress

•Cost and materials

Most people look for mattresses with coils. They are affordable and readily available.

Prices range from $200 to $1,000. Consumer Reports says all but the cheapest are durable, and all coil materials and coil counts more than 300 are adequate for support.

The luxury-mattress market has stepped up in recent years to entice sleep-deprived customers with such brands as Tempur-Pedic ($1,200 to $6,000 for queen), which touts a foam core that conforms to your body, and Select Comfort, whose Sleep Number beds ($1,000 to $4,700 for queen) have adjustable firmness. Both of these claim to insulate you from a restless bed partner’s every movement.

Another high-end option from Sealy and Simmons is synthetic latex, which conforms to your body but springs back quickly. It is designed to eliminate pressure points that cause tossing and turning. A queen-size mattress retails for about $3,000 to $4,000 at D.C. area department stores.

•Comfort and Support

Doctors used to recommend firm mattresses for everyone, but many now say that a slightly softer one can ease aging joints and pressure points. Mattresses have become softer and thicker in recent years, so you might have to buy new sheets, too.

Another tip from Consumer Reports: Go to a store to test-drive mattresses and determine the level of firmness and comfort you need. Take at least 15 minutes to lie on a mattress, spending 5 or so minutes in the positions you normally sleep in. Wear comfortable clothes, and bring your own pillow if you want — salespeople expect it.

Also consider how comfortable the top layer is. If the stitching that binds the ticking to the top pad forms a large quilt pattern, the mattress will feel softer. If it’s smaller, the mattress will feel firmer. “Pillow top” models offer an additional layer of softness.

•Those Pricey Add-Ons

Although mattress manufacturers encourage customers to buy a matching box spring, consider a lower-priced one or keep your old one if there are no signs of wear.

In recent years, hotels have tried to entice customers by upgrading bedding and pillows, adding foam or featherbed toppers to mattresses to make them more comfortable. Depending on materials, these range from $100 to thousands of dollars.

Featherbeds, which give the effect of a pillow-top mattress, are made of feathers and down and can be removed and shaken out. They can also be easily washed, if this is a concern to you. Alternatives in the same price range include memory foam and latex toppers. However, these are all unnecessary if you buy the right mattress in the first place.

All mattress manufacturers encourage you to buy mattress pads to protect against liquids. (For mattress care, they recommend only spot-cleaning with mild soap and water to prevent damaging the material.)

Costs for pads range from $12 for standard polyester fitted styles to about $50 for thick egg-crate foam versions.

Pillows: Do you want size or support?

A pillow is a personal purchase and something few of us do often enough to know what we need. What to consider when buying pillows:

•Allergies

If you are allergic to those fuzzy soft feathers known as down, don’t buy a down pillow.

Hypo-allergenic down pillows are available, and other alternatives include foam, polyester and buckwheat, some of which mimic the feel of down.

•Size

Think about your size and the way you want your bed to look. Many people like to buy bed pillows of varying sizes to create a layered, full look but may sleep with only one or two.

•Support

To test the firmness of a pillow in the store, don’t be afraid to manipulate it –– squeeze it and mush it into shape.

If it immediately collapses, it’s a soft pillow; if it takes some pushing, it’s more supportive. Back sleepers need a lower, softer pillow to keep their necks positioned comfortably.

Side sleepers’ necks are positioned much higher, so they need a more supportive pillow to keep the spine properly aligned.

•Care

Using pillow protectors can double the life of your pillows. Zip pillows into them and then cover with a pillowcase.

SOURCES: “How to Buy a Mattress Without Losing Sleep,” January 2008, Consumer Reports; Mark Benson, marketing manager of Pacific Pillows; National Sleep Foundation; Tim Oakhill, executive vice president of marketing for Simmons.