I want to refurbish a metal folding chair with seat and back cushions. The wood base for the seat and back cushion are in very bad condition and I have to replace them. I was thinking about using plywood for the seat base since the original one is flat. The back cushion base is curved though and I don't know what material to use to replace it.... The original looks like compressed wood. Is that what you recommend? How do I give it the curve I need? Thanks!