Don't buy the soft foam as it will just disintegrate. It will feel stiff at first but will get
softer after a little while. I just made two cushions for our kitchen chairs. I used some
foam that I had saved from equipment packaging. Glad I did. I also had to glue them
together with contact cement because I didn't have a piece big enough. Then cut it to
shape. I used a box cutter for cutting the foam. I didn't bother to make a first cover.
If I was making a square cushion, maybe I would have. This was some odd shape...
sort of roundish.
The foam was 1.5" thick so I had to cut some strips for the sides. The Clover binding clips
was a big help when I was constructing the cushions. Best $$ I've spent in a while.
I just used some cotton fabric I had on hand. But you could use some canvas maybe.
There are some nice ones out there.
If you're planning to wash the cover, you might want to preshrink the fabric and put
put a zipper. I hate zippers so I just sewed mine shut. LOL
I used a zig zag stitch plus fray check on the seams.