I agree with Kyrill, but I will add my two-cents worth from my own experience. I am between an A and B cup, 38B to be precise as far as bra fitting goes. I bought myself several push-up bras and hard shell bras, but they all have problems. The one that I like best is a soft material bra (JC Penney has then), which provide support, but allows some growth.
The problem with a hard shell, at least for me, is that my breasts are not heavy enough yet, so they do not push down the bra. These bras alwasy ride up and are annoying. When I was taking estrogen / progesterone, the bras would be a bit uncomfortable too, especially on my nipples. I did not think of that until Kyrill said that, but he is absolutely spot on. He knows his bras. I have a soft one, which stays down and is does not bother me. I enjoy wearing it all day.
Hopefully, my breasts will start growing again soon (could not happen fast enough). I would love to have the problem of my breasts growing out of my bra all of a sudden and need a bra buying emergency.