I have used underfelt supplied by Banks, but it is very hard to cut, and I always take skin off my right hand middle finger when cutting the underfelt with metal shears.
I use the same stuff on the engine bulkhead, with dark grey floor vinyl covering it in the engine side.
I use EvoStik spray adhesive to hold the underlay in place inside the cockpit, and self tapping screws to hold it to the bulkhead.