The Mark II is what we do.
Under that cushion you'll find two things, a cardboard liner that has pulled apart, and a sling that supports your butt across all the seat springs, rather than just your pelvis.
The sling is made of a rubber/fabric that has likely torn into many pieces. Remove them and note where they are attached. I have a woman that sews up 2 pads for each front seat. Using hog rings or button thread, attach the sling to the same spots. She uses race car suit cloth. A folded over layer cannot be penetrated by hog rings, but they do grab the material.
The cardboard is designed to help the seat frame from cutting into the cast foam seat cushion. Using Gorilla Tape to piece the cardboard back together, with the shiny side under the springs, cover that layer with another to ensure solid resistance. These things will help a lot with seating height and seat shape.
Barry Wolk
Farmington Hills, MI
C5681126