I was so excited, after having two kids pretty close in age, to feel like my body was my own again. I had mentioned treating myself to some nice underwear, so DH gave me a gift card to Victoria's Secret. I went in, all excited about buying some nice bras for once in my life, instead of the cheapo ones from a department store.
I get a handful of bras in my size--B--and head to the dressing room. After a few minutes the woman working there taps on the door and asks if I want some help, so I let her in (since I've had two children and everyone and their uncle has seen me half-naked). "Oh, honey," she says regretfully, "I think you might want to go down a cup size."

So, now that I am in the height of my womanhood, feeling happier with my body than I've felt in awhile, I've been demoted to training bras.

Actually, I found some bras I love, modestly padded, that hide the pre-pubescent breasts that I'm rockin' these days.
Sorry I don't have better news from you based on my experience. I hope it's different for you and you totally keep the perky Bs! Oh, but WHILE I was breastfeeding--man, those were the most incredible breasts ever! Like bowling balls, round and firm and perfect. Wish I coulda kept you....