I'm a plus size girl (42 chest 38 waist if you want some idea of my size) and I practically live in skirts
I love gothic lolita fashion so most of my skirts are puffy and worn with a petticoat underneath. Some say it emphasises their size but I find it make my waist look smaller (I don't have a very defined waist) and they're what I feel most comfortable in therefore I feel the most confident.
On the chafing in the summer.. I have a few pairs of gymshorts that I wear underneath my skirts or sometimes I wear bloomers.
My weight is rarely much of an issue to me, I just make clothes to fit or modify patterns to be bigger if needed