Mattresses have changed since you last bought one

If you haven't bought a mattress in a few years you'll notice that the market has changed. On the plus side, there are more choices in mattress types, including combinations such as hybrid innersprings and varying levels of foam over adjustable-air beds. And you'll see more retailers, including web-only sellers with great prices and generous return policies. Other surprises, however, are less welcome. Here are five new twists that you may not be aware of:

You have to climb aboard

The models in Consumer Reports' mattress Ratings average nearly 12½ inches high, ranging from the foam Ikea Matrand (just 7 inches high), $400, to the pricey Duxiana Dux 515 innerspring, $7,595, which is 20 inches high. Add in the usual nine-inch box spring or foundation (the Duxiana's height includes it), and your bed could easily top 30 inches including the six to seven inches of room beneath the frame. Major brands sell low-profile foundations, typically about five inches high; Tempur-Pedic sells ones as slim as two inches. But still, you may need a step stool to get into bed.

Old sheets don't fit

Extra cushioning on many new models is part of the reasons that newer mattresses are thicker. And those extra layers may mean your old sheets won't fit, since standard fitted sheets probably are difficult to pull over the corners of mattresses 15 inches or thicker. (Among our tested mattresses, the recommended Stearns & Foster Estate Scarborough Luxury Firm, $1,575, and six other innersprings come in that range.) Other than selecting a slimmer mattress or using a second flat sheet in place of the fitted, expect to buy deep-pocket sheets for a thick mattress.

A gripe about grips

Older mattresses could be rotated, flipped, or both to allow for uniform wearing of the springs. But today's innersprings, often "hybrid" with layers of foam on top of the springs, don't allow for flipping—so the grips that invariably lined the sides of old innersprings aren't always there on a new one. Foam mattresses often have no grips, because you can't flip them, and rotating the bed offers no benefit. And if the bed's firmness is different on one side than the other, as with adjustable-air and some foam beds, you can't rotate or flip the bed.

A plastic smell to dispel

When you buy a foam mattress or one that includes foam, you'll probably notice the smell of plastic in the room where you place the mattress. While it may seem overpowering at first, the smell is temporary. Our advice: Once the mattress is installed, leave the sheets off and open the windows for several hours, weather permitting. If you still notice the smell when you go to sleep that night, remove the sheets again in the morning and ventilate once more, which should suffice.

Prices that bounce around

While not all mattress sellers have prices that vary, prices at department stores and mattress chains can vacillate by 50 percent or more. We routinely warn readers to wait to buy a mattress at such stores until a holiday weekend and to watch for advertisements—or, better still, insist on the lower sale price as a condition for buying, even when the mattress you want isn't on sale. If you buy on impulse, you could have missed a sale by just a few days and end up kicking yourself for not doing some research beforehand.

Need a new mattress?

Our mattress Ratings currently have almost 40 models, and we're getting ready to test even more. (In addition to our performance Ratings are survey-based Ratings of mattress brands and stores.) Be sure to see our mattress buying guide before you narrow down your choices.

—Ed Perratore (@EdPerratore on Twitter)