If FIAT, they are VERY inexpensive new. Try and find the Brembo brand discs. I had never turned one down when I ran my Lancia Scorpion, it cost more...
There are some extensive threads on this topic elsewhere on the site. The old 2 part foam is as you note quite rigid. BSS has(d) a bead type seat kit...
I am in need of a new seat. My current one is many years old and is made of two part foam and duct tape. It consists of a pad for my back and another...