It is best if you can find a skirt that measures the same at the top to the bottom. If you take the waist band of most skirts it will just about be the same as the bottom. Pick sturdy fabric with not much stretch.
Old or second hand skirt [make sure it has a zip or button opening]
Stuffing [I use plastic shopping bags]
Take off the waist band if needed, turn inside out, pin and sew across top[straight stitch and zigzag], open zip or buttons then pin and sew across bottom[straight stitch and zigzag]. Turn your skirt back out through the zip or button opening, stuff through this opening.
Will post a picture when I finish stuffing it, saving all my plastic shopping bags with holes in them.