Glamorize makes some supportive bras for larger sizes. I got mine through mail order from JC Penney but lots of online stores carry them. They are not that expensive, at least for bras.

www.breakoutbras.com was really nice about getting information about my issues with bras and recommending several types to try and then mailed them to me. One of their recommendations is my favorite bra ever but right now I'm wearing the cheaper glamorize because of money.