I'd recommend that your first step is to re-do the plastic. Find some 15 mil somewhere (or similar thickness) and spread it out over the entire surface and even up the concrete walls. This helps to keep down any moisture seeping up from the ground. Tape all seams.

Next, seal all holes through that subfloor with expanding foam and/or zip tape (or similar). Also, seal any air gaps around the sill plate.

Next, spray foam IS the best in a lot of ways. It would cut down on any draftiness by 99.9% and increase the warm feeling of that floor by a ton. BUT - it's expensive. You wouldn't need to do it at full depth to get desired results. But 4-8 inches would be good.

If spray foam isn't in the budget (call some local places), go with some r-21 to r-30 fiberglass insulation. Faced or unfaced it probably doesn't matter too much as long as the humidity stays low-ish in that crawl space.

I'd also recommend getting an accurate hygrometer down there for a week or two to see what the levels of humidity are. If they're consistently low, you can probably stop here. If they are consistently above 60% or so, I'd recommend a dehumidifier that has it's own pump so you can just turn it on and not have to fuss with it when dumping it out.