First bra stories advice and help?

I am flat chested and in 8th grade going to hs. i have little buds but i really want a bra . how should i ask my mother about it. what if she says that i dont need one then that will just be embarring. my brother teases me about having nothing. and my cuzin whos younger than me already has way bigger then me and when we do sleepovers with her 2 sisters who are 14 and 15 wth bras too, i feel left out and very uncomfortable. one time one of them said ewww you dont wear bras!!!!!! they talk about bra shopping and everything and i'm just left out. In school too everyone is already devloped and i think that when the girls talk about it in the locker room and stuff they look at me or weird and that even makes me feel worse. please can you help!!