This is a seat done as suggested in Jweb's post.
The springs were replaced by foam of various densities - it took a couple tries to get it comfortable. The depth of the back foam is about half that of the springs.
This is the seat - not quite done yet. Will probably repaint the seat frame to the same color as the covering.
Another view
The plywood base for the bottom and upright of the seat is covered with the same carpet as the floor and edgebanded in the seat material