I thought I understood the size chart, but since it didn't work out the first time, here are my stats for others perhaps like me:
122 lbs, 32DD.  I bought the medium, thinking usually the 34D which it would translate to, would work.  The band was fine but the cups were too small.  Ordered the large and it'll do.  It's not overly compression based, which was fine for the purpose I wanted it for - very hot weather in FL in Summer, but breathable.