Hi BruceB,
The first place I would start (in case you haven’t read it already) is post #1 here which has the basic information, steps, and guidelines that you will need to make the best possible choice.
You have some good options available in the Berkeley area and some preliminary research on the phone should tell you which of them can make a mattress that is custom sized. They are listed in post #2 here.
Almost all of the latex you will encounter will be Oeko-Tex certified and most of the the memory foam and polyfoam that is made in the US is CertiPur certified (although not every store will be listed on the CertiPur site even though the materials in the mattresses they carry are made by a CertiPur certified foam manufacturer).
Since a mattress is only as good as it’s construction and the quality of the materials inside it … I would focus on the materials inside it more than on the brand.
Hope this helps and if you have questions along the way don’t hesitate to post them on the forum.
Phoenix