Do not buy the Tempur-pedic brand mattresses. There are tons of memory foam mattresses on the market that are essentially the same exact mattress for a fraction of the price.
I've got a memory foam mattress that we bought a few years ago, and for us it's great. Memory foam is all about the density of the foam. The density will be measured in pounds. The more dense, the more firm the mattress will be.
There are great deals on memory foam to be had online and in stores. I believe we bought an Ashley furniture brand memory foam mattress and spent less than a grand on the king size. The comparable Tempur-pedic mattress was almost $5000.
Tempur-pedic is the mattress industry equivalent of Bose. Their product is no better than anyone else on the market, they just have the best advertising and marketing department in the industry.