I did my own upholstery in the FM during the Z71 conversion in 2015-2016. I love to do all I can myself, and this is no exception.
My mother was a self-taught amateur upholsterer, and I learned from her. So I know just enough to know that it is possible.
I'm not going to go into step by step detail. There are all sorts of tutorials on the web. But here's the run-down:
Take the seat apart enough to remove the coverings. Take pictures as you go. Capture plenty of detail. Most are held onto the frame with hog rings. Spread those and throw them away. You will need to use new ones, with hog ring pliers, to reinstall later.
Take the upholstery apart in sections. Take plenty of pics. I use a seam ripper to cut the thread, and separate the panels.
Take the time to study how it went together, and ponder why. That's how you develop a plan of how to recreate it.
Buy material. trace the pieces, and mark out any lines that will need stitching. make reference marks. Take note of which direction the seams are facing.
If there was welting around the seams, you can either reuse it, make new, or eliminate it. Welt hides the seam and gives it a finished look. Some is extruded vinyl, and some is material sewn over cord.
Sew your panels together into sub-assemblies, then stitch the assemblies together inside out. Then turn it right side out and install it.
Here are a ton of pics:
Cheap machine
Seat bottom showing frame
Old stuff
There are runners with metal rods in them. They get hog ringed to the seat frame to hold parts of it down into the foam. That's what gives it that bucket seat look.
Separating with a seam ripper
Welting that I made