I've just switched to a couple old bras that are a little more stretched out. You could also try tanktops with a shelf bra (I do that a lot for PMS anyway), or the nursing bra. Also, you may be more comfortable if you go hippie-style, wear a thick sweatshirt and skip the bra completely once in awhile, if you can. :-)
maternity bras have lots of give, congrats! how far along are you? when are you due?