Bra is nothing but an undergarment. Wearing or not wearing has not effect on your health. It is worn more for support and comfort. Of course of last few years use of bra for cosmetic purposes has increased.
Primary function of breast is to make milk for the baby, and it also serves as a secondary sexual organ.
Even if you do not wear bra, it will have no effect on shape, size or function of breast.
So take out doubts from your mind, please do what you think is comfortable for you.