The saleswomen at Nordstrom were very helpful, although the first one first said "Okay, looks like you're between a 32 and a 34," at which I raised my eyebrows, but hey, she had the tape measure. Then, after trying a few things in the 34DDD range, she went "Hmmm" and fetched the larger-busted saleswoman, who determined that no, 32 was right. Between 30 and 32 really, but closer to 32.
Sadly, the bra I liked best does not come in my size. The 32DDD was close, but not quite there.
I did come home with a bra (also a 32DDD, but wireless, so the cup size is less important). It's not perfect, but it's better than my existing bras. And the information gained from this expedition will be very helpful in hunting about online.
Also today I got the car's oil changed, dropped off a few things at Goodwill, and went to the library. Go me.