@Gene5 @Ana2038 @Quincy
Homeowners insurance in California does not cover businesses, as you said, and if your agent does not offer business policies you can definitely get cancelled if you even mention STR, which is a business. Some companies will add an STR business policy to your existing homeowners. May I suggest you confer with an agency that has multiple companies and have them locate a business policy for you. Indeed, as you said, homeowners insurance in California has become extremely costly - ours doubled twice in 2 years, and is something we've had to budget for, very carefully, along with property taxes....
Hang in there and persist in the research and shopping. I found that it is easier now than it was a few years ago. Best of luck to you, and let us know what happens!