Not sure if your query is about handling the fabric while you sew or to prevent the cushions deteriorating in use. If the latter, when I make cushions, I make them 1.5cm bigger than I want, trim the seam allowances slightly, turn them to right side (you'll need to be careful pressing the seams open), then do a sort of french seam on the right side, 1.5cm in to enclose the raw edges.
If it's handling while you sew, you could fuse strips of lightweight interfacing around the edges. You could still use the method above. I wouldn't use pinking shears.