2nd time moms- nursing bra question?

pinklilly122

 I have gotten to the point a normal underwire bra digs into my stomach when Im sitting. So time for a new bra. My question is should I buy nursing bras now? (Im due Nov,11) and if I do, what size should I buy? Right now Im in a 36B, so do I buy that size or a cup size bigger or what? I know there isn't a way to know for sure how much bigger they will get when my milk comes in, so how does this work? In case you couldn't tell Im a FTM lol