I've replaced the seat bottom leather on several Gen II Explorer/Mountaineer driver's seat bottoms. While in there I typically find broken springs an less than perfect, but still serviceable seat foam.
Warning: This is a time consuming job.
1) The seats are held in by 4 bolts. Raise the seat (if power) a bit and move it forward and backward to get better access to the 4 bolts. It's a good idea to first get under the vehicle and spray a penetrant on the bolt threads and even wire brush the exposed threads to remove rust and dirt to make removing he bolts easier. You will also need to remove the plastic covers off the rear bolts (assuming they're still there) and also remove the inside seat belt bolt & track (T50 IIRC) as it's attached to the seat bottom.
2) Once the seat is unbolted, tip it forward to get access to the electrical connections (air bag wiring, seat belt reminder switch, and power seat power supply).
3) Now the seat can be removed from the vehicle and the plastic trim panel(s) removed (Phillips screws). The knob and the cable disconnected for the adjustable lumbar support and the seat back can also be unbolted from the bottom. The large lumbar adjustment knob can be popped off with 2 large screwdrivers, or pry bars. The cable has a connector that you push together and unhook once the adjustment tension is relaxed. Then remove the bolts that hold the seat back to the seat bottom.
4) With the bottom removed from the seat back, flip it over and remove the 4 bolts that hold the seat to the mounting base. Now you are ready to remove the seat cover.
5) The cover is held to the metal frame of the seat with wide plastic clips that are part of the cover. You can pry them loose from the edges of the metal frame with a long screw driver. Then there are a series of "hog" rings (maybe 7-8 per side) that pull the covering tight to the seat frame. The hog rings need to be cut or twisted off to remove cover from the foam and seat frame. Once the cover is off the foam can be removed and replaced or built up as desired. I suggest you remove the foam to examine the condition of the seat springs and to repair them as necessary.
6) You will need a supply (15-20) new hog rings and either a good pair of strong needle nose pliers (or a good set of hog ring pliers) to reattach the seat covering to the frame when your done.
New foam and seat covering can be purchased from
www.theseatshop.com but this stuff is not cheap (around $100 for foam and around $200 for new leather). They also offer vinyl substitute covers for around $130. I would think an automotive seat shop count replace broken support springs. I've found the quality of theseatshop's products are excellent and they are very helpful.
Tip: Consider placing a supporting fabric (like burlap) between the seat foam and the wire springs to give extra support to the foam.
Reassembly is the opposite of disassembly. If you attempt this job plan on spending a minimum of 1/2 day to complete it.