Poor shoulder posture? Should I wear a brace?

I'm a 16 year old girl and I'm a bit taller than average - I'd say about 160cm or something I'm not sure at all. My back hurts a lot and for a long time my shoulders have been slouching forwards and I have a forward neck posture as well. I've seen a doctor who said that it was just because I'm tall but I would like to find a way to help me correct my posture. I was looking at shoulder braces but I'm not sure which to get and was wondering if there are any disadvantages to this like muscle loss because through lightly researching I've seen this come up as a problem; and also, can I excersise with the brace to prevent that? Thanks for the help