Hi pokorourk,
In case you haven’t read it yet … the first place I would start is post #1 here.
I wouldn’t research mattress construction … that could be a learning curve that takes years. I would focus more on researching the knowledge and experience of the retailers you are dealing with and their willingness and ability to provide you with the information you need. Once you have read the overviews (not studied them) so you have some basic information (probably more than most mainstream mattress salespeople) and you have a good idea of the guidelines about what to look for and avoid (major brands, chain stores, any retailer that doesn’t fit the criteria here and any mattress where you can’t find out the quality of the materials that are in it) then it’s time to start testing mattresses to see which types of materials and mattresses you tend to prefer.
The better options I’m aware of in the Phoenix, Tempe, Tucson area are listed in post #4 here and it includes 3 of the members here which are all among the best value in the country.
As the guidelines suggest … I would tend to avoid most of the places you have visited and focus on the better options you have available to you.
Phoenix