I am thinking a sectional that you can bring down piece by piece, or something you can bring in boxed and then assemble yourself in the basement, like some Ikea modular furniture.
Did you check your local building and fire codes?
I ask because some building pr fire codes demand that you install an egress window if you are to use the basement as living area. (personally I would consider one anyway... it is always a good idea to have two ways of escaping the area in case of emergency)
I don't mean to be intrusive but 24" sounds like too narrow an emergency access in my opinion. I think in a home we should always be prepared for worst case scenarios, i.e. what if someone gets hurt or sick for example and paramedics need to get a stretcher down there?
Where I live I probably couldn't even get a permit to finish a basement like that without the egress.
Anyway, my point is: if you install an egress window you will have an opening of about 42" x 48" to bring in furniture.