Happy New Year! You may have already completed your bathroom addition by now, but this is still a relevant question as my clients often ask for contractor recommendations so I wanted to post a response. I have personally used Alward Construction for a large renovation/addition, and they are fantastic. They are based out of Berkeley. I highly recommend reaching out to Keith Alward and his team.
780 San Luis Road
Berkeley, CA 94707-2030
I highly recommend Karen Dinardo with Dinardo Design & Construction. She has extensive experience with bathroom and kitchen remodels in the Oakland Hills and her work is top notch. She is very reliable and detail oriented, below is a link to her website.
Best of luck with the bathroom addition!