Hi puttslayer,
The first place I would start your research is the tutorial post here which has all the basic information, steps, and guidelines you will need to make the best possible choice. It also includes the answers to many of your questions
Once you are at step 3 then the better options and possibilities I’m aware of are listed in post #2 here which also includes Texas Mattress Makers who is the newest member of the site (they were just added today) which means they are among the manufacturers or retailers that I think highly of and believe compete well with the best in the industry.
If you follow all the steps in the tutorial post you will end up making a great choice. As you will also read … outside of careful and objective testing for PPP (Posture and alignment, Pressure relief, and Personal preferences), the most important part of a mattress purchase is to make sure that you know the quality of all the materials inside your mattress (see this article). The quality guidelines I use are in post #4 here and if you find out and list the information about all the materials in the mattress in the forum (and they will provide these to you) I’d be happy to comment on the quality of the materials inside the mattress or the mattress in general.
Phoenix