I am 5’2 130 lbs and my stomach is not flat! I purchased a small, but if you’re looking for some space in the waist I would get a medium. The small fit but a little snug on my belly perfect fit on my legs. Over all I was still very comfortable even though the waist was a little snug on my not so flat belly lol I just gained some weight I’m used to wearing an XS and weighing 110/115 so now that I’m 130 I think a medium if I’m tryna fit comfy and a small if I want it nice and tight and fitted. Very stretchy material