I'm 120lbs and 5'6", I went with a small cause that usually works for me. If you look at the zipper in the pictures you'll see that the fabric gaps a bit around it, yours will do that too and I hate it, the waist is just a tad tight (I have a 25.5in waist and about 36in hips), but that could be fixed by going up a size.

My biggest complaint is that the color is COMPLETELY different than pictured. I thought I was getting a spring perfect blue (the one pictured), but in real life it's a dark royal...

In the link is the true color of the pants. [...]