If you just want coverage, a tank top or camisole can go under another shirt. A sports bra is also very comfortable and can help to smooth things out. Also, a soft-cup bra (no underwire - you don't need it) is good if you want a little bit of lift and support.
I'm not an expert on bras, but since you have smaller breasts you don't need a bra with as much support. And you could wear thinner, more comfortable bras that let your nipples show through when you wear tight-fitting tops. That's always sexy to see.
I love bralettes! Or lace no padding. I find that they make my breasts look way better, and you can find some that are sexy. I go on journelle, or the mesh/ lace from American apparel, bralettes from urban outfitters etc.
Honestly I go to this store what they have adult training bras 3 for 10 for comfortable days. Any 28 band push up bra on days where I want to look fuller. 28 so it stay in place and has good support. Sometimes 32 is too big.
At vs they have nice bras but if you're smaller than 32a or want cheaper bras for less than $50 they have really small bras (smallest is like 28aa I think) at Aerie/American Eagle's bra section that are only like $30