I find that something with an empire waist, which sets right below the bust, is flattering, and there are a lot of cute, young looking tops out right now with that type of styling. Neckline can make all the difference as well, and a v-neck (thought not too deep!), scoopneck, and halter are my favorite choices. Add a cute cami underneath tops as a style note and for extra coverage if needed!
For bras, I love Calvin Klein’s t-shirt bras (which you can get at Macy’s, and not for too bad of a price on sale), but if you’re looking for something on a little tighter budget, I find that you can’t go wrong with Target—some of the Xhiliration bras are decent and cute, typically start at a 32A, and cost very little (often under 10 bucks). Just be sure to ALWAYS try styles on before you buy.