As ccluster suggested, I have moved to sports bras or very supportive bras that I have had fitted - this is my second pregnancy though and have gotten to the point I won't skimp on bras.
For what it's worth, I'm sold on nursing camisoles since although not as supportive as most bras, they solve the large tummy exposed issue for me without buying specialty nursing shirts. I don't think I'm a total prude but I'm not comfortable with lifting my whole shirt in public and found the "hooter hidder" type devices a pain.
Get a sports bra they are comfy and stretchy
Well every woman's pregnancy is different. For example I am 12wks 5 days and my bust size went up 3 cup sizes. You bust may go up one size or several. Its a tricky situation but in the end your comfort is most important and honestly that to me is not wasting money! Bad support in a bra leads to bad back pain and misery! Also as you get farther along you do end up being bigger around too! In the end its up to you on how comfortable you wish to be! Best of luck!
Get an adjustable bra now nursing bras are more for convenience when actually breast feeding not for your boobs growing
Well its really hard to say as when your milk comes in you may need to buy an even bigger nursing bra...so you can buy a nursing bra now just incase it does still fit later, or you could buy a normal bra and find out how big of a size youll need later... and you may grow out of bras a few times as you still have a long pregnancy ahead... its really hard to say for sure as its still early?? every woman is different...