Even if your BBs don't get bigger you will still need maternity bras so you can unclip the cups for feeding. And Myer is great for fitting - even if you don't end up buying your bra there they will still do a fitting for you.
During pregnancy I loved the Lovable 'suddenly shapely' bras - they provide the same shape/ support as an underwire bra but they don't have the actual wire. And the yummy mummy maternity bras are pretty good too, but it will depend on your size and the shape that you like. good luck!