repair of original front bucket seat

Lots of time it is just the foam broken down.

There are small wires that are interwoven in the burlap and tied on either end with paper rope under the foam in the originals. They add lots of overall support! You need to disassemble carefully and assess how to repair them. Legendary interiors has some good videos to show you how but never include those supporting wires in them. I could suggest the type that you may find on the side of the road as markers for utilities with little flags. You may need to soften them with some heat first. You may have broken springs and or a cracked frame but until you take the cover and foam off it may be hard to tell.