Hi epicsmash78,
The better options or possibilities I’m aware of in and around the Modesto/Stockton area (subject to making sure that any mattress you are considering meets the quality/value guidelines here) are listed in post #7 here.
The list for the San Francisco/Berkeley/Oakland areas is in post #2 here and for the San Jose area is in post #2 here if you would also like to include some additional retailers or manufacturers in your research that are a little further away.
Phoenix