Hello, sister Jamie.
Your progress is exceptional for only 2 months. A lot of new sisters on their NBE journey get very discouraged in the early stages when they go 3-4 months without any notable progress, but I don't think you are ever going to have that problem. Something important to remember as you go is that genetic females breasts grow during puberty. Your body already went through puberty and part of the NBE process is tricking your body into undoing the puberty you already went through and starting over to go through female puberty, instead.
As for bras, where one when you think you need or want one. I will recommend, however, that you not trust sizes, and definitely not size calculators. For the first good bit, a simple sports bra will be more than enough, but as you get further along, and should you be blessed with success into the C or D ranges, get a professional fitting. It might seem awkward the first time, I know it did for me. If the people working the boutique are professionals, they will take care of you and make sure you get the right bra that you need for a fair prize, and they will even help you size and adjust it. They will take care of you.