I can't find the thread now but thank you to all the people on the bra size thread who are correcting us women who have been wearing the wrong size bra. I was dubious, but after wearing a 36c do years and measuring 31inches round the ribcage, I have just taken delivery of my 32DD bra which fits like a glove.. I expected ott to be really right and uncomfortable, but I can hardly tell its there it is so comfy.
It's definitely the place to start - bodies can be tricky if you are pear shaped or hourglass though. I had to go up a back size to get a basque to fit but because there are so many clips it gets away with it! be prepared to try a few sizes.