Hi B.,
I had problems finding good supportive nursing bras, too. I have a small rib cage with average size breasts, but to fit me right, I have to wear a 32F. I ordered mine online at barenecessities.com and they fit wonderfully. I can't remember the particular brand I got, but on the website you can search specifically for nursing bras. I got underwire ones and they worked out great for me. They have excellent bras. Some of them are a little pricey, but a good bra is worth it in the end. Most of them range from $50 - $80. I know it sounds like a lot for just a bra, but it was so wonderful to find one that fit and didn't make me feel like a saggy grandma (no offense to the grandmas out there!). By the way, most of us don't get our bras small enough around. I used to think I was a 34 DD. But by the time I got it right, I was a 32F, and really could use a 30. The weight of our breasts should be carried by our ribcage, not our shoulders. Good luck!