Hi Gynna,
It’s great to see that you are looking at all the different parts of the “value” of a mattress purchase including the quality and durability of the materials rather than just focusing on the “showroom feel” of a mattress. I wish that more people shopping for a mattress were as thorough as you are 
If you can find out and post the information listed here about any mattress you are considering I’d certainly be happy to make some comments about the quality and durability of the materials and components inside it and the mattress “as a whole” and let you know if I can see any potential weak links in the mattress.
While it’s not possible to quantify the sleeping temperature of a mattress for any particular person with any real accuracy because there are so many variables involved including the type of mattress protector and the sheets and bedding that you use (which in many cases can have just as significant an effect on temperature as the type of foam in a mattress) and on where you are in the “oven to iceberg” range and because there is no standardized testing for temperature regulation with different combinations of materials … there is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range. While there are many different types of memory foam and some can be more breathable and “temperature neutral” than others … memory foam in general can tend to sleep warmer for some people than other types of foam materials (such as polyfoam or latex) that are more breathable.
The better options or possibilities I’m aware of in and around the Austin and San Antonio areas (subject to making sure that any mattress you are considering meets the quality/value guidelines here … which it certainly seems that you are) are listed in post #2 here.
I’m looking forward to finding out what you end up deciding … and of course any comments or questions you may have along the way.
Phoenix