Well, there's no law against owning bras in different cup sizes. You might try a larger one, fill it with something and see how the look works. I'm not on hormones, but I fill a AA well enough and normally wear that because frequent wearing seems to add a certain degree of body sculpting. I do have a pair of "cutlets" I sometimes wear in my A cuppers, though. With my size and figure, I'd probably look the most balanced with a C or even D cup, but I don't want to overdo.
I've never found catalog bra size specs at all reliable. By trial and error, I finally realized I was a 36 and that usually works. A personal fitting sounds like a good idea.