This has been on my to-do list for ages. We spend a lot of time on the front verandah between now and March. It's comfy enough, but I do like a soft seat. Foam from Clarke Rubber was a surprising $41.00 - I thought that quite expensive. Material from IKEA around $26.00 - gorgeous heavy canvas. Not a completely neat job - I wanted something I could get off easily enough to wash - which meant an opening on the long side rather than the short to avoid fighting to get the foam back in each time. I used large press studs because they were to hand, doing it again I'd give valcro a whirl.
Overall verdict - quite pleased.