Hi! maybe this will help
It will depend on the type of cushions you have. You can sew them similar to a pillow case and finish after you put in the cushion. Another option is to add piping along the seam all the way around where the top & bottom meet. If you have photos or can provide specifics on the cushions, you will get better answers.
Can you use the cushions you have and reverse engineer them to make new ones with some foam and fabric from Joanne or another craft store?
Trying to do that..want a "skirt" around them for something different..thanks for your in
Hoping this will give you some inspiration
Have you seen this youtube video? It may be of help to you
How to Make Chair Cushion Covers. Wash and iron your fabric. Measure and cut a piece of fabric for the front piece of you pillow. Make the piece 1 inch wider and longer than your cushion. Cut a piece of fabric for the back of the pillow cover. Make the width the same size as the cushion, plus 1 extra inch. The length should be the size of ...