Hi placcy,
You may have seen these already but the better options or possibilities I’m aware of in the larger Bay area region (subject to the “value” guidelines I linked in my last reply) are listed in post #2 here and for the area in and around San Jose are listed in post #2 here. These would include all the better options I’m aware of that are in reasonable driving distance of San Mateo.
The most common cause of a sore lower back in the morning is choosing a mattress that is too soft.
There are several component mattress choices in the lists I linked that would give you good options after a purchase to fine tune the support and/or comfort of a mattress by either rearranging or exchanging layers or components and these can certainly be a good idea … especially for those that are closer to the “princess and the pea” than the “I can sleep on anything” end of the scale and who are more likely to need some fine tuning after a purchase.
Phoenix