Take it to a pro?
Mel, I had a Goldwing seat recovered by Bob at Stitch Surgeon here in the city. He does excellent work, and is very reasonably priced. Am sure he has various grades of foam in stock as he recovers motorcycle, sled & ATV seats all the time. Here's a link to a current Kijiji ad he's got up:
Spending my daughter's inheritance one motorcycle at a time.
Bikes currently owned: '91 Honda Gold Wing with sidecar, '92 Kawi KLR650 with Enduro sidecar, and '94 & '97 KLR650s.