Hi karen123,
The first place I would start your research is the tutorial post here which has all the basic information, steps, and guidelines that you will need to make the best possible choices … and learn how to avoid the worst ones.
I don’t recommend specific brands or mattresses because brand shopping is among the worst ways to choose a mattress. The name on a label isn’t important because outside of testing a mattress for PPP (Posture and alignment, Pressure relief, and Personal preferences), the most important part of choosing a mattress is knowing the construction and the type and quality of materials inside it so you can identify any weak links and make meaningful comparisons between mattresses regardless of the brand name on a label. All manufacturers have access to the same types of materials and all of them make lower quality and higher quality mattresses in a range of budgets (see mattress firmness/comfort levels in post #2 here). I’m always happy to help with “how” to choose but the specifics of “what” to choose is up to each person based on which mattress is most suitable for them in terms of PPP and is the best “match” for the parts of their personal value equation that are most important to them.
Once you reach step 3 in the tutorial the better options and possibilities I’m aware of in the San Francisco area are listed in post #2 here. You are fortunate because you have many good options in the area.
Phoenix