How many newborn sleepers should I have?

Cam • My sweet little pea is here! Born June 1, 2016 🎀
I've been pretty confused buying baby clothes because everyone says she will grow out of newborn super fast. Dr said she wasn't a big baby so I'm sure newborn size will fit her at first. Right now we have 4 one size gowns and 2 sleepers and probably about 7 onesies. Should I get more sleepers? My mom said she would need more. How long did your newborn stay in NB size?