Hi CranialCrusader,
Thanks for the kind comments 
Ashley sleep used to have a house brand with latex in the comfort layers with an inch of polyfoam over the latex in the quilting (the maximum amount of polyfoam I would usually recommend as being “acceptable” in a comfort layer). This was over a HD polyfoam core. The three models in this line were useful for testing what a latex comfort layer felt like as I had the specs of these mattresses.
On a recent trip to their site, I discovered that now they have a new line that also has latex in the comfort layers but it has 2" of Syn Tex over the latex. “Syn Tex” or “engineered latex” is usually “code” for polyfoam manufactured to feel like latex and to “give the impression” that people are buying latex. This puts it over my “limit” and makes it far less useful even for testing purposes as people would be feeling the qualities of the polyfoam more than the latex. The old models are no longer available (confirmed with a call). Their house brand … according to the people I talked with … are manufactured by Sealy although some of their models use Zinus trademarks.
I think I may have misread the earlier post in this thread and posted Austin manufacturers. There are a few options for Houston that I know about but not as many as other parts of Texas. My apologies to the OP for not listing them earlier. They include …
NOTE: there is an updated and more complete list for the Houston region in post #2 here.
http://www.houstonmattress.com/ Doesn’t list exactly what mattresses he produces but uses quality memory foam at least. Would be worth a call to see what type of variety they make and if they use latex.
http://www.antiquemattress.com/index.htm or http://www.texasmattress.com/ Seems to focus more on odd sizes and mattresses for antique beds but I see no reason they couldn’t make regular sizes as well. Says they make latex as well as other options.
There are also some local wholesale manufacturers which may make a mattress that is suitable for what you are looking for and which may be available through local outlets (you would need to call them or email them for a list of the retail outlets). These do not sell direct to the public but through retail stores but there is often good value in more local “retail direct” outlets …
http://www.sleep-designs.com/collection.htm
http://ammattress.com/index.html No latex that I could see.
http://www.goldenmattressinc.com/ContactUs.aspx
http://www.noahsmfg.com/index.php?page=mattresses-categories
http://www.citymattressfactory.com/ These are a manufacturer in Dallas with good value that sell direct but I do know they also ship to various retail outlets in Houston. May be worth a call to find out where some of their recent Houston shipments have gone.
Some retail outlets that carry latex that would be useful for testing different latex mattresses and layers include …
http://www.newliving.net/non-toxic-organic-natural-mattress/ Carries OMI and Royal-Pedic. Both very high quality but IMO much too expensive. Useful for testing and “duplicating”
TranquilityMattress.com is available at DomainMarket.com. Call 888-694-6735 Has Dunlop and Talalay choices which would give a clear idea of different latex comfort and support layers
“House brands” can be made by many manufacturers (some very good and some not so good) and their value would depend on who made them and the materials they used. Some are well worth looking at and some are much lesser value. The materials inside them and the transparency of the outlet that sells them will say much more about the quality and value of the mattress than the brand.
Hope this helps in your search.
Phoenix