For lining, I always use something that is the same weight or lighter than my main fabric. The fabric store should have a section of fabric called “apparel linings.” They’re usually polyester and shiny. They’re perfectly fine to use but I tend to use just a regular lightweight cotton because it’s usually easier to care for (washable), easier to work with (doesn’t slip around) and feels more comfortable to wear. I wouldn’t think the flounce is going to have any lining to it. I’d love to see a picture when you finish! 🙂