Hi BigWind,
If your Tempurpedic mattress still has the law tag it should tell you which mattress it was. Otherwise the height would probably be the best way to tell.
If you test a mattress very carefully (and hopefully using the testing guidelines in the tutorial) and you are testing for more than the more subjective “comfort” or the “showroom feel” of a mattress then in “most” cases and for “most” people it would end up being “close enough” to your actual sleeping experience that only relatively minor find tuning may be necessary if anything is necessary at all (see post #4 here) but for those that have have some history of having difficulty in finding a mattress that “works” or have more challenging circumstances (such as health or back issues or an unusual body type) then the odds of making a choice that doesn’t turn out as well as you hoped for would be higher and the return policy can be a much more important part of the value of a mattress purchase.
Phoenix
PS: I see we were posting at the same time and I missed your last post in my reply. If your old Tempurpedic mattress was the Classic then a firmer mattress would certainly seem like a good idea and the firmer Tempurpedic Contour Supreme may be an even better reference point that would also be well worth some careful testing.