I wear the Bellas almost exclusively. Last year's X smalls fit me perfectly. I like the low waist and compression. I am 5' 1" and weigh around 107. My waist is smaller in proportion to my hips (26.5 to 36). But when I got a new pair of Bellas this year, they seem tight. I have a little muffin top, which I attributed to lack of weight training, age, etc. But, still... I have always worn x smalls in the Terry's. So, I am working to get rid of the extra flab. I have one pair of Sheebeest triple s shorts and those fit perfectly (x small). I too, thought about sizing by the hip measurement, but if I get smalls, they are always too big, esp. the chamois.