As a temporary measure, you could make a ramp out of plywood/chipboard,
perhaps covered with something like carpet offcut for aesthetics and
grip. You'd need to make sure it's well secured to avoid it
disappearing under a sofa, or a human getting an unexpected sledge
ride, but if you're going to carpet the stairs, you can drive screws
into them without *too* much concern.

[Posted in FML 7811]