Pooks - I'm a member of the Brooks Cult, but honestly you may need a firmer seat. I had a terrible time until I finally got a Terry Sport years ago. (they don't make that one anymore) It was firmer and smaller than the gel seat I'd had on my bike before.
I ride a hybrid, very upright, and I'm on a Brooks B67 (like Mimi's). It is incredibly comfortable. You have 6 months to try it with all your money back, it's hard to go wrong with that. I would worry that continuing to ride on a seat that causes tailbone pain will just make it take longer to get the pain to go away when you finally do change seats.
A seat only takes a couple days to reach you from Wallingford...
(and the springs on a B67 don't make any noise. The shackle of the frame of mine was noisy for a while, but the springs are silent!)
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