I was always wearing A-cups although friends never thought I am an A!
but, well those were the bras who fitted best, possibly 'cos I am very small around the chest as well!
I am wearing now a C-cup and solely breastfeed (besides of solids @ lunchtime and some water) my daugther for nearly seven month!
I was worried about it too, not too much 'cos of my size, but 'cos of the fact that my mother and my aunt "weren't able to breastfeed". OH never understood why I was worried about it. and now, I also can't see the reason, why my mother and my aunt weren't successful, probably they weren't patient enough, or with household and other kids they didn't have the time!
it is important that you let your LO suckle as much as it wants in the beginning to stimulate your production! alright, I was glued to the sofa, watching tv-channels up and down all day long for the first three month, but it was worth it