Your Breast care nurse may be able to supply you with a special 'Berlei Bra' for free (donated by Berlei to BC patients, post op.) It is a quality soft bra that does up from the front instead of the back, so you put it on like a jacket.
Failing that - KMart and other shops have a lot of 'pull over' bras (Ahaa Bra is one of them) and they often come in a pack of 3 - white, beige & black!
I hope you are able to find one that suits you. xx