Like I said, long day so I didn't spend a bunch of time on this lol. Basically think Motorcycle seat. Just grab some piping from a fabric store and the material you want to wrap around the piping. The first pic is a basic way to do it, heck I added more in than you would need to do.
This second pic shows a few more lines, honestly to get all that piping on the top would be a delicate and tough job but I was thinking about doing like a tuck and roll pattern here (like the old vinyl seats in those cars we used to drive) which would be much easier. You just need to use a thinner layer of foam against the material and sew those lines in to cause the bumps or "tuck and roll" and then that top piece wouldn't stretch nearly as bad either.
I hope you get a little idea what Im trying to say lol, my brain is pretty fried from today and I hope it didn't get all jumbled up.