Hello. Try a lightly padded bra, no pushup, just one of those comfortable cotton bras with padding. If you want your chest to appear fuller you could wear ruffled tops or any top with a pattern that stands out. With that I suggest you wear a solid colored bottom, preferably high waisted jeans or a skater skirt to tuck your top into. This will make your chest look bigger that it is.
Can you give us more info?
Wear a cami and if that doesn't help wear sports bras i usually wear those all the time and i'm a little mature for my age im starting 6 grade next year e.o but i wear them. The more girly looking ones are annoying and i HATE!
Loose tops
Nothing, why put up with the discomfort of a bra when you don't need one? If you want the modesty of wearing something wear a light husband beater (girls tank top)
If your boobs are big enough, try something with pads. That will smooth out your nipples. If not, wear a training bra, and then a tank top over that. That should smooth it out enough.