I have been looking for a bench cushion for the bench that is on my deck. It is such an odd size that it would have to be custom made and would end up costing was too much. So I found video on YouTube from Melanie Ham. You can search" Melanie Ham How to Make a Bench Cushion in 2 Hours". However, it took me longer than that, of course! She had the easiest directions.
I bought fabric and the high density foam cushion at Joann's. The back cushion is from the original cushion. The bottom cushion had been damaged.