Bikini tops are a great, ,simple addition to your costume.  Available in several colors from sizes Small through XL.  These tops do appear to run a little big.  The back strap has a clasp which is not adjustable for going around the body, but if you needed the strap to be tighter, I imaging you could just tie the two straps together to your comfort.  Your hair will cover it while dancing anyways.  Just a thought from Auntie!