KLNoel,
What we did was to get Latex foam like in the photo below. 4 inches or better is best. We then used and electric knife to cut it to size. Jill then sewed a cove for it that is the same as our other cushions. We found a foam store close to us, but you can find it on-line and order it.
Because we only used 3 inches, we then also put a layer of that egg carton type mattress topper on it. We change this about once a year. And we cover it all with a set of fitted sheets. Worked GREAT for us! and the cost was way less than going out and having one made to order.
I think it would be great to also use the Froli system to support it, but our mattress is in 4 parts and goes up and down, so they are hard for us to use.
Just some ideas for you.
Greg