You're not going to get magic boobs overnight especially from just PM. Take your time, really. You might react fast but you will NOT grow super charged crazy speed.

I'm quick to react to hormone changes and still took months to even reach budding stage. Bras can be problematic, don't try to logic your way with it, it wont work as every manufacturer has their own ideas with sizes. Going for sister sizes is a smart idea, a lot of bras have weird af band size which is often much larger than what the number says. The band size and your band size will rarely match.
When I was slimmer, I could depending on brand go down to 36 and 34, butI measured 38" for a long time. Now I measure 42" but on Ewa Michalak brand the band size is actual centimeters and their bands are not stertchy so itgoes way closer to how its supposed to be like.
Also when you say "no more than B cup", note that bra sizing isn't universal. There is no THE B cup, B cups on each band size have different width, depth and volume. Bra sizing works as a percentage which is typically either 12% or about 12,5% which happens when using metric or imperial sizing to differentiate between cups. Also, note that the letter and number are a ratio of band and bust measurements. Which means that all D cups are in a same ratio, but bigger bands size D cups have larger volume. And the way manufacturers deal with that differs.
Trial and error, reading reviews and so on will help a lot.