Rebuilding a bench seat

Hi Everyone,
I was going to install a pair of buckets to replace the current bench but have changed direction on that.
I want to keep my current bench seat but the drivers side is super soft / cratered like a 400 pound man was driving it for a long time. I sink 6+ inches down when I sit on it (175 lbs here) and it bounces like a trampoline over bumps.

Being a short guy it's a ***** to drive this way.
If it was stiff / hard then I'd be at the correct hight for comfort and safety (sight-line, pedal reach, ect.).
Does anyone here know how to rebuild a bench seat? I would think that the springs are shot along with the foam and anything else that's under the vinal seat cover. I looked for a seat but everything I see for sale, which isn't much, are nasty and in need of rebuilding themselves so I'll redo my own.
I've search the internet and really don't find anything useful.

I just don't know the first place to start for all the parts, tools and steps in refurbishing mine.

TIA for any experience on this!
Dean