There are lots of discussions on insulating the subfloor. Most agree the fiberglass batting is not the best as it holds moisture and mice love it.
I used rigid "pink" foam board 2" thick. It is about $20 a sheet at the big box stores. Some use adhesive, or precise length screws with fender washers driven into the subfloor but not through it.
I don't know much about reflective bubble foil insulation. I see it placed in windows to reflect the sun's heat. But I do know people use it.