If you have easy access you could do rolls of fiberglass. Otherwise blown insulation. However, in either case you want to make sure you don't block any eaves vents by installing channels to keep them open. Go with unfaced fiberglass if you use rolls. No need to remove the vermiculite, it is still providing insulation and if you know it doesn't have asbestos in it there isn't any problem leaving it. Removing it would be a huge mess.