As opposed to repairing the foam, if you can get your hands on a passenger seat you can swap the foam over from the seat base. Passenger foams are generally in a lot better condition as they are sat in less....
From my build thread....might come in useful....
The bolster on my drivers seat has been badly knackered for a long time (which is a very common fault with this style of seat as I am sure you folks know) and I was actually on my third drivers seat with this car, so I took the opportunity to deal with it. First of all, big thanks to my friends Amy and Gaz for sourcing a pair of seats in the right cloth for me. They came out of a three door, and obviously Kermit is a 5 door. But I had a plan (I didn't know if it would work, but it was my plan and I was sticking to it).
Here is my original drivers seat:
As you can see, its had it. This was unsightly, and uncomfortable for me to sit on as the metal bar was digging into my leg.
So first things first, lets get rid of the back rest for now - that is the one bit of the seat I will reuse...
This turned out to be suprisingly easy - you carefully remove the covers either side, remove a clip, and undo one T30 screw either side, and then the back simply lifts away.
Next you have to remove the seat fabric, this is where it starts to get harder...
The fabric is held down with an assortment of clips, spikes (that are folded down and you have to lever up) on the seat frame, and a wire that attaches at the rear on either side and runs all the away around the base of the fabric. Finally the fabric is secured to a number of rods running through the seat foam, and its a bugger to disengage these...
Now the fabric is out the way and we can see the root of the problem...
So we will sling that foam in the bin.
Its actually very difficult to completely remove the fabric from the seat base (you can see in the photo the staples that go through the metal base holding the fabric in place), so at this point I elected to use the drivers side seat base of the three door seats Amy sorted me, and the foam from the passenger seat base. Here we can see the base itself, with the fabric still firmly attached at the back:
The passenger seat foam was perfect, so i placed that on the base, reconnected the fabric to it, and reattached the fabric to the seat frame. Even thought the base I am now using is from a 3 door, it is actually identical to a 5 door one, so I now mounted the backrest on the seat and reattached all the trim plastics and handles (and picked out the most intact/unmarked/undamaged plastics from the three seats during build up). Leaving us with this:
So to recap, that is the foam from the 3 door passenger seat base, the base and cloth from the 3 door drivers seat, and the backrest from my five door drivers seat! Aka - Frankenseat. 
One perfect drivers seat with no sagging of the bolsters and no damaged fabric. Its so much more comfortable!
Kind of pleased with myself for having done all this. In total it took about 2.5 hours, which involved the full strip down of 3 seat bases, and the rebuild of one seat. Now all I need to do is get my hands on some form of wet vac so I can shampoo the seats properly.
Next up... Bought fast road brakes all round yesterday off of a gentleman on edition who lived close by, and I have a new head unit to go in, once I pull my finger out and do so.
