Plus sized pregnant lady here too!
Bras - not sure where you are located but Lisa'a Lacies in Frankston, Victoria have a great range and are fairly priced. They can be bought online or from the store and have a fantastic return policy. It's the only place I buy bra's now.
Clothing - Undercoverwear has quite a few items that are stretchy and will go from pregnancy to post pregnancy with ease.
Maternity Revolution gets my vote too as well as Mums n Bubs Maternity, Just 4 Mums Maternity Wear and Ebay.
HTH's!