Bikini sizing help.......?

I am top heavy -_- & I was wondering how big is too big to buy a bikini? i want it to fit right and also be roomy & if it is too big i could shrink it in the dryer right? especially because they come the same size i cannot get a smaller bottom and a bigger top its all the same size so how many sizes is too big to go up? the top & bottom both have strings so i could tighten it and it would be fine if it was a little big right?