Hi sleepless,
Ditto to what cviz said. If you email them or (preferably) talk with them they will give you the specific details of every layer of their mattresses.
The 4 lb memory foam in the Cloud series will soften faster than their higher density foams but the Supreme would probably be less risky than the Cloud Luxe because there is only 2" while the Cloud Luxe has 2.75" on top.
The Dallas list is in post #4 here.
Although I don’t think that Original Mattress Factory has memory foam and I don’t think that Sleep Craft does either (although they do have one mattress that mentions memory foam), the four manufacturers there would certainly be worth calling to see if they either have or could build something along the lines of what you like. I have talked with and think highly of all four of them.
Therapedic in their Ecogel line and Restonic in their Tempagel line also has combinations of memory foam or gel memory foam with either high resilience foam or latex under it in some areas of the country and you could check the retail finders on their site for local retailers and then call and ask them if they have any mattresses that fit your criteria. The Restonic retail finder is here and the Therapedic licensee for Texas is Sleepinc and you can contact them here.
The minimum guidelines I would suggest for a memory foam mattress are in post #10 here. In terms of the density/quality it would depend on the specifics of the mattress but none of the Sleep Science mattresses are CertiPur certified.
Phoenix