Hi GJBenn,
The Select Foam is one of the better online options for memory foam which is why I included them in the online memory foam list in post #12 here.
They designed their mattresses to have a similar feel and firmness to the various Tempurpedic models so that you could get a sense of what each one felt like (although it won’t be exact of course because each type of memory foam has different characteristics).
NOTE ADDED: Select Foam was a member of this site but because of ongoing customer service issues and delays their membership was terminated and I would read the warning here before considering them.
Memory foam and stomach sleeping can be a little tricky and risky because of the risk of hammocking. In general … stomach sleepers would do best with the thinnest firmest layers that provides good pressure relief in their other sleeping positions. The "key is “just enough” memory foam in the comfort layers for pressure relief but no more than you need … especially on your side.
Like the others on the list … they will give you some guidance in your selection and testing the Tempurpedics to see which one is most suitable would also be more accurate than “theory at a distance” and would also help them help you better. Your own personal experience and careful testing specifically for pressure relief and alignment for at least 15 minutes fully relaxed (and perhaps longer on memory foam which takes time to soften) is always more accurate than trying to build a mattress by specs (either yours or the mattress).
As you have seen … there are many better options than Tempurpedic with equivalent quality of foam and much better value.
Phoenix