Beth,
I think my experience has been similar to Angie's. I'm closer to your measurements though, just a couple inches taller but otherwise the same. I have a medium but I should have ordered an extra row of snaps. The extra row would have made the pouch work better early on and kept the pouch from hanging too low as the fabric stretched. But the medium on the tightest setting works fine for me now that my baby is bigger and I'm wearing heavier clothes with the colder weather, both of which make the fleece stretch tighter and keep it in position better.