I was studying my daughters' expensive sofa that seemed saggy and beat down on the upper cushions that go behind your back. I unzipped them and saw that they were stuffed with pieces of batting. I got some bed pillows she was throwing away that had the same type batting and used them to add to the stuffing. It came out great!
I did this...sort of. My brother gave me his expensive couch when he moved. It had about 6 throw pillows (large to medium) n addition to the couch pillows. We got a beagle, and as it usually goes. He chewed of some corners on the throw pillows and laid on the back couch cushions; mutating them over years. One day I seam ripped the back cushion (where you can't see) and filled it with the chewed pillows, and other used poly fill. I even put in cut up tee shirts (heavy) for the base to keep them upright. Work great!