Worked on the seat, a bit, last night (well, the bottom anyways)
Ima usin' a piece of 1/2" plywood
...a piece of 1" closed foam
...a piece of 1" soft foam rubber
...& (2) different kinds/styles of black vinyl type stuff (from Walmart)
For this one, Ima gonna try ta make 'er a bit more/kinda 3D (ish)
So, when sewing the "side strips" to the center piece, I added a couple of "channels" of material (just some scrap "jean" type material)
...to slid a couple of pieces of wire (with bent ends, for use with screws) into
...then, put 'em thru "slits" in the soft foam
...& finally, secured 'em down with a couple of screws
* The idea is that these "wires" goin' thru the "channels" & screwed down, should "pull" the "seams" down
...helping to create a 3D situation
** Also, I cut the top piece of (soft/white) foam ~1" bigger
...so, it could/would "wrap" over/around the stiffer (black) stuff (creating a softer edge)