Most attic access doors are made from thin plywood and rarely seal tightly, so they do little if anything to stop cold attic drafts from influencing your heated living space below. The solution is an insulated air trap above the access door.
Foam insulating board is ideal for this project because it’s inexpensive and easy to fabricate. Use pieces of the board to build a box that’s slightly larger than the folded stair unit above the door. The top of this box should be hinged so you can open it to enter the attic.
Use foil backed duct tape to hinge the top, make the other joints, and to seal the unit to the attic floor. A few dollars and a little effort will make a big impact on your utility bill.