If you're comparing the options of buying a complete bed made of memory foam or sticking with your original bed and putting a memory foam mattress topper on instead, you might need to exercise caution if you're favoring the latter choice. Yes, you want the benefits of the memory foam, which are great nights of sleep, excellent support, and a mattress that "remembers" and returns to its original shape in the morning. But it's how the foam topper interacts with your existing mattress that might be the problem.

What makes a memory foam bed work so well is a combination of things. The top layer of foam is what softens when exposed to body heat, changing to adjust itself to your contours. But the memory foam in lower levels of the mattress retains its shape and firmness, since the heat doesn't reach down that far. That quality of support provided by the lower level of the foam stems from its high density; in some cases as much as 8 pounds per cubic foot. This very firm support is just as important to the function of the memory mattress as the softening and changing of the upper level.

And that's where the problem comes in with a memory foam mattress topper. If it's not sitting on something almost as firm as the lower levels of foam in a regular visco memory foam mattress, then the topper doesn't have the support it needs. Combine this with the fact that many regular mattresses have places where they sag to some degree, and a layer of memory foam on top will sag right along with them. This will pretty much negate any benefits that could have been derived from the memory foam topper.

All of this means that you might want to think twice about simply buying a memory foam mattress topper and sticking it on top of your regular bed. Unless you've already got a very firm mattress, completely flat with no sagging anywhere, then the foam in the topper won't have enough underlying support to provide you with the benefits of the best memory foam mattress. If you're going to spend the money anyway, you might as well go for the whole bed. That might be preferable to never getting all of the benefits you were hoping to gain.