Debbie, I am 5'3 1/2" ( I won't post my weight as I have 5 pounds that need to go somewhere else) and I got the small size. The length is perfect for me because I like pants to go over the shoe. The waist, just like Barbara says, does not dig into my waist. I was worried before I ordered them, about the pants staying in place, since they are low waisted; but they stay put. I wore a pair of mine around the house and they work just fine; they feel like a second skin on me. I haven't worked out in them yet because I'm saving them for the new series.
Did I help you spend more money? ;-)