Hi redsail,
You are fortunate to be in the San Francisco area because there are many good options in the area. I’m sure you’ve seen this but in case others read this thread they are listed in Post #2 here.
It’s always best to use the type of box spring or foundation that the mattress was designed for and that you tested it on. Innerspring mattresses are usually (but not always) paired with a boxspring that has flex and foam mattresses are usually (but not always) paired with a non flexing foundation. If you test a mattress that uses one type of base and then put it on a different type it will change the feel and performance of the mattress. While you don’t always need to use the box spring or foundation that comes with the mattress …it’s important IMO to at least use the right type and one that is the same as you tested the mattress on. There is more about the different types of foundations and box springs in post #2 here.
Phoenix