Cellar insulation with Airtec / bubble foil

I currently have a cellar with exposed joists that I'd like to insulate to prevent heat loss from the room above. I'm looking at something like the Airtec double bubble foil insulation.

As boarding the cellar ceiling isn't really an option due to some exposed pipe work, there seems to be two ways of using this type of insulation:

1. Cut the insulation and staple between the joists (leaving an airgap between the foil and floor above).
2. Fixing the insulation to the downward facing part of the joist, bridging the entire surface of the ceiling (using foil tape to seal where necessary).

I'd rather use option 1 if possible but am concerned that some heat may leak through the joists themselves (cold bridging) using this method. As there is some heating pipe work at the same level as the bottom of the joists, would I need to ensure that the insulation has some clearance from the pipes?

Which option would be best?