Bra question and my mom. ?

Just tell her you are a B cup and that the A cups are comfortable... When you go shopping, choose the bras you like and tell your mom that you would really want to buy some like that. You can make a compromise and buy one bra that you like and let your mom pick the rest. Sometimes you can't get permission for everything at the same time so it's better to go step by step. :) Hope I helped!