Hi PDSTEX,
Welcome to the Mattress Forum!. Just in case you haven’t seen it yet … the first place I would start your research is the tutorial post (linked in the top right corner of the page and underneath all of my posts) which includes all the most important information, steps, and guidelines you will need to make the best possible choices all in one place.
They use good quality materials and are open and transparent about the materials in their mattresses and are among the better online sources for memory foam mattresses (which is why they are included in the list in online memory foam list in post #12 here).
I also think highly of Houston Mattress factory and they use high quality materials in their mattresses. You are not the first to mention the fact that all their mattresses are covered in plastic though which can certainly make them more difficult to test. They are knowledgeable and experienced and they do have good options available after a purchase if for some reason your mattress doesn’t turn out to be as good a choice as you hoped in terms of PPP so that can offset some of the risk of making a choice that isn’t ideal because it was more difficult to test how they would feel in your sleeping experience but it does lead to a little more uncertainty compared to showrooms where what you are testing is the bare mattress without the effect of the plastic.
Phoenix