Hi kvothe,
The first place I would start your research is the tutorial post here which has all the basic information you will need all in one place along with the steps and guidelines that can help you make the best possible choice. It will also help you learn how and why to avoid the worst ones including the major brands that normally use lower quality materials or are not good value compared to many other manufacturers that are available to you that make mattresses that use better quality materials in the same or lower price ranges than the major brand equivalents.
You have listed some good criteria and I would use the testing guidelines in the tutorial post to find a mattress that is the best “match” for you. There are too many variables, unknowns, and preferences involved in a mattress choice for anyone else to make a recommendation for a mattress based on “theory at a distance” that can possibly be more accurate than your own personal testing and experience. Nobody else can feel what you feel on a mattress (see mattress firmness/comfort levels in post #2 here).
Outside of testing a mattress for PPP (Posture and alignment, Pressure relief, and Personal preferences), the most important part of a mattress purchase is making sure you know all the specifics of what is inside it (see this article) so you can identify any weak links and make more meaningful quality/value comparisons with other mattresses.
[quote]Beyond mattress recommendations, I notice a general trend on this site to promote latex beds. Why is that?
Please help me understand what kind of frame or foundation I may or may not need.[/quote]
I don’t recommend or promote any specific type of material and every material has higher and lower quality versions so I would “recommend” that each person choose the mattress and the materials that they prefer in the highest quality version that is available to them in their budget range (regardless of whether it’s memory foam, latex, polyfoam, or any other material or component in their mattress). Having said that … latex is a very high quality material that has many benefits and once they’ve learned about it and tested it in person (and it’s often not available in mainstream stores) many of the members on this site have chosen it because they preferred it over other materials that were available. There is more about the pros and cons of latex in this article.
Phoenix