I tried on the dress that was returned at my store in xxs p, i would not have based on reviews but my stylist asked me to try it on. it does look nice, you just have to cinch it all the way. perhaps most people do need to size down. for my 115 lbs, 30dd, 26.5in waist, i wouldn't go up to xs p... to give an idea. 
material is nice and sturdy. give ti a try!