Our attic door is in our daughter's room, and needs to be insulated to eliminate drafts.

It is a standard 6 panel door like the bedroom and closet doors. I'd like to insulate the interior of that door with a thin, but efficient material.

What is the best way to insulate it, while also keeping as much of the full width of the door opening as possible. We do use the attic for storage and require access to things up there year round. As soon as you open the door, there is a square landing space, and a 90 degree turn to the staircase. Outside the door, is where my daughter's radiator is located, so the door does not swing completely open (maybe only about 110-degrees). So, every available inch of clearance is important to access.