I have spent much time in the past six months shopping for a new mattress all over San Francisco and Marin & Sonoma counties. I ended up going with Sleep Train in Novato. My salesperson, Pat Carlin, is also the store manager.
Pat is fantastic. I found him to be perfectly honest, mellow and not the obnoxious salesman you dread to find in such situations. I asked Pat dozens of blunt, hardcore questions about mattresses to help me make my choice. He was always perfectly forthcoming and direct. He can answer any question you can think up about mattresses.
Also, I found that Sleep Train offers the best policies by far. They have a 90-day guarantee that can't be beat; you can sleep on your new mattress for three months, then, if you decide not to keep it, you can either receive a complete refund, or a free one-time exchange. Free delivery and pickup, even for an exchange. They usually have some kind of bonus promotion too (right now it's a free down comforter).
I will head back to Sleep Train and Pat any time I need a new mattress in the future. I have already sent tons of people to him; he's a superstar.