I am a smallish plus-size (I can often, but not always, wear women's XL garments, 1x is usually where I fall but sometimes 2x). Furthermore, I have ex-rugby-player thighs -- I was a prop, which relies on thighs and core muscles, so my thighs are still quite muscular and large.
Standing normally, I've got a Venus of Willendorf thigh situation going on, is what I'm saying. If, like wendy says, I push out my butt and arch my back, I can make a thigh gap magically appear. Bodies are just peculiar.
Back when I wore skirts and dresses a lot, I had a great collection of pettipants to wear underneath. Comfy, lightweight, inexpensive, and smooth.