I wear a medium in Iman clothing. I once bought one of her maxi dresses in a small and realized I needed a medium to make it not skin tight. I just don't want skin tight. I am about your weight, a little more, shorter and would wear a size 10 in pants. I would suggest you try the medium unless you want it skin tight. If your waist to hip ratio is so different, you may just have difficulty with any skirt, unless it has a tie waist like the olden style where we had drawstring waists. My sister would get her waists taken in by an alterations lady. Not sure what skirt you are looking at but remember the models on TV do not show the back side very often because they are putting them in too tight of clothing. When the model says they are in a small, I always wonder. When the plus size model says she is in the large and it is skin tight like a sausage, I know this is too small. Even with Iman's line, HSN is doing the too tight sausage look on the models.
Detachment isn't the absence of love but the ability to take care of yourself in the midst of someone else's choices.