It is important to stop the air leaks to minimize heat loss. If you can do this your 99% of the way there! Heat loss due to diffusion (heat lost when it passes through a material) is extremely minimal when compared to the heat lost due to air leakage. If you just insulate (with fiberglass blankets for example) it won't do much, the insulation just filters the air as it passes right though, carrying moisture with it that can lead to lots of other problems!
We manufacture a folding attic stairway cover (The Batticİ Door Folding Attic Stairway Cover) that we market on-line.