After ripping out remaining staples and laying out the smelly pieces, I began to trace the old pieces onto the new materials.
Here is the old seat with the side seams ripped.
Here you can see a detail on the sides where an extra triangle shape is added.
Layers:
Tracing out the dissected vinyl:
For the layer between the vinyl and the foam I used an old sheet, but I should have used something with stretch.
The burlap:
The foam:
Coming soon: Reconstruction