Hi ersendil,
Berkeley Ergonomics mattresses have been mentioned many times on the site and a forum search on Berkeley Ergonomics (you can just click this) will bring up much more information about them. They make some very good quality mattresses with good value.
A forum search on Sleepworks will also bring up more information about them (you will need to scan past posts about other retailers with the same name). I have talked with them on several occasions and think highly of their knowledge and experience and the service they provide to their customers.
A mattress is only as good as the quality of the materials that are in it and most of their mattresses use latex which is among the highest quality materials available so I don’t know if I would say they are lower quality. I don’t know the details of their innersprings or how they compare to BE (which use some very high quality European pocket coils) but they are certainly better quality/value than mattresses made by the larger manufacturers. A forum search on naturalmattress will also bring up more feedback about them as well.
Both of these are among the better options and possibilities in the San Francisco area which are listed in post #2 here but to make meaningful quality/value comparisons between specific mattresses you would need to know the specifics of each mattress you are comparing both in terms of the design and materials in each as well as how well each of them matched your needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and personal preferences).
You are certainly looking at some good options IMO
Phoenix