How often should you shop for a mattress? "We'd suggest that consumers evaluate their own mattresses for comfort and support every five to seven years," says Nancy Shark, of the Better Sleep Council. It's not that the mattress isn't durable.

"The bed that you bought at 30 or 40 is not going to be comfortable at 40 or 50, because as we age, our bodies become more sensitive to pressure points," says Tod Marks, senior editor at Consumer Reports.

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Spend at least 15 minutes lying on a bed in a typical sleep position before you buy it.

RELATED LINKS: • What you need to know about mattresses • More shopping stories

Tips

The 15-minute test. Spend at least 15 minutes lying on a bed in a typical sleep position to evaluate it. When Consumer Reports did its last mattress evaluation in 2005, people tested beds for 15 to 20 minutes, then took them home and slept on them for an extended period. "We found that the 15- to 20-minute impression that people had jibed with their long-term satisfaction," Marks says. It's important to note that every mattress tested had supporters and detractors. "No single bed was perfect for everyone."

Do I have to spend a fortune? The 2005 Consumer Reports evaluation found that people should expect to spend at least $800 for a queen mattress. "There's no need to spend thousands upon thousands," Marks says, "because from a standpoint of durability, all but the most cheap mattresses are apt to hold up over time."

Beware the "myth of the comparable." With so many different stores selling mattresses under so many different names, it's common for a retailer to say it has a comparable mattress to something you've seen at a competitor. Consumer Reports checked out some of the claims. "And in most instances, most of the models that claim to be comparable, they're not," Marks says. If you're overwhelmed, you might want to stick with one of the big S's (Sealy, Simmons, Serta and Spring Air) because they're more widely available.

Negotiate. Marks suggests that shoppers approach the purchase as if they were buying a car. Tell the salesperson you don't want to overpay. Ask if it's the regular or sale price, and what is the best sale price they've ever had on this mattress. (Often, Marks says, they're marked up about 40 percent to 50 percent.) "Then say: 'OK, I'm not going to buy the mattress unless it's at your best sale price. If you won't give it to me, I'll shop elsewhere.'"

Ask about "comfort return." Make sure the store offers a comfort return policy — if you don't like it, you can return it. Get the fine print. Finally, see if they'll cart away your old bed.

Take the hotel test. Some of the more upscale beds are being cross-marketed in hotels. If you're interested in the Sleep Number bed, consider your next overnight lodging at a Radisson — the hotel chain has an exclusive deal with Sleep Number. You can find Tempur-pedics at many hotels; for a list, visit www.tempurpedic.com, scroll to the bottom and click on Hotel Locator.

Myths

Firmer is better. You've probably always heard that a firm mattress is best to relieve lower back pain. But a 2003 study reported in the British medical journal the Lancet found that people who had slept on medium-firm mattresses for 90 days felt better than those who had slept on firm mattresses.

Coil count and cashmere are key. "You can ignore things like coil count," Marks says, "and all these claims [about] cashmere, wool — about fancy stuff in the ticking. It doesn't matter." As for coil count, Consumer Reports says any number above 390 in a queen-size mattress should be plenty.

A super-low promotional rate is your friend. Beware of the ads that promote really cheap mattresses — like a queen for $200-$400. "Those are usually awful and offer very little comfort," Marks says.

WHERE TO SHOP

Inner-spring mattresses are available nearly everywhere mattresses are sold. Here's where to find a few of the other kinds:

• Sleep Number: Available at Select Comfort stores. Visit www.selectcomfort.com.

• Tempur-Pedic: Available at many mattress retailers. Visit www.tempurpedic.com.

• Online: Find more information on mattresses at www.consumerreports.org and www.bettersleep.org.