Why draughty? That'd be one of the first things to fix.
The attic rooms of my house came with about 10cm of fibreglass wool between the roof tiles and sloping ceiling. Somehow the installer had managed to stuff it in there from the loft area. I felt it might compromise ventilation, and it didn't seem very effective.
The method I used was during a refit, with 50mm celotex foamed to the roof timbers, plasterboard over. Obviously a lot of mess and bother, but it's made the rooms very easy to heat and keep warm. A 400W heater keeps the temperature in a 6m x 4m room. at about 17C when it's freezing outside.
Probably of little interest to your pal . . . ;-)