Yes, you can use cotton instead of wool, but cotton batting will increase the dimensions of your cushion, since it does not compress as much as wool. In that case you would need to reduce the size of your foam to get the same size cushion. A rough guess might be to reduce each foam dimension by 1/2” for a 1.5” thick cotton batting, but you would have to experiment to see what works. Note: you don’t need the ticking fabric with cotton, though a thin cover sewn around the cotton would make it easier to stuff into the outer cushion cover, as cotton tends to stick to everything it touches. Another important consideration is fire resistance – wool is naturally resistant to flame, while cotton is not.