How to insulate heat ducting?

My new 44-year-old house has an oil-fired hot air heating system, and the ducting is non-insulated. I would like to wrap insulation on the outside of the ducting, in the crawlspace and other exposed areas, but they get pretty warm. What would be a good and safe insulation product?

Also, this particular home does not have any insulation in the walls (lucky me). I know some about blown-in insulation, but another unique feature of this home is that all the rooms have the heat registers at the base of exterior walls, not the floor. By base, I mean, like 6"-8" off the floor. Will the heat from the ducts in the lower walls pose a problem when the blown-in insulation is added?

Thanks in advance - TomR