I'm currently wearing a 36B, but of course they'll get bigger. I just don't know how much bigger. How do you know what size to get?
Yeah I would not go out and buy an expensive nursing bra right now--until after baby is born and your rib cage may change size, and boobs will be going through more size changes... and then settle down.
I prefer cheap, soft sports bras like these: http://www.amazon.com/gp/product/B001GP269Q/ref=oh_details_o01_s00_i00 until about 6 weeks postpartum. They are comfy enough to sleep in and hold a nursing pad in place, cheap, and work for engorged breasts! I did order a size up, and they are super comfy right now. I find it easy enough just to pull the bra down or up to nurse in....
I like nursing tanks in theory, but find that they are often sized weird... like too small or too big. And then they can ride up... maybe nice for summer if I can find one that fits right... but otherwise I like these cheapo sports bras and a tank... kind of the same effect. :)
I loved the tanks after my third. When she was 3 months old, though, I got mastitis. I didn't realize the tank was causing a pressure spot, and continued to wear them. By the time my 4th was born, I had a pretty chronic problem with 2 places because of it. I was wearing the Gilligan O'Malley brand (target), and, though I loved them, I just had to stop wearing them all together. I still, at times, have issue with those 2 places. Even after I stopped wearing them, I seemed to be really susceptible to mastitis after my last baby.
So...what brand are you looking at?
i am waiting to see what size to get, too! i got a couple sleep bras from target that are just sized medium. they have a tank i want, too, but it is out of stock. but i really, really would like an extremely pretty bra, since i'm going to be breastfeeding for awhile, i hope. my bust size hasn't increased so far (also 36B), and if it doesn't then i can't get the elle macpherson bra i wanted (http://www.journelle.com/elle-macpherson-becoming-daylight-maternity-bra.html), in which case i'll get one from here http://www.cakelingerie.com/online-store/ or here http://www.hotmilklingerie.com/ (they come in smaller sizes).