How Do I Make a Staircase More Accessible?
Steps are inherently inaccessible; there’s really no getting around that. The chairlift would make the stairs less inaccessible, but only to people who are otherwise able to walk on a flat surface. Folks with large mobility aids like a wheelchair won’t be able to use the lift. Not to mention that you'll need to replace/reinforce the staircase in order to make it safe for the chairlift.
Since getting rid of the stairs entirely isn't an option, I would look into replacing them with a staircase that has long stairs that are also extra deep and have a riser between steps. This won't make it accessible for wheelchair users but it will make it less inaccessible to people who use crutches. Extra long steps make it easier to balance and distribute your weight and the riser prevents the crutch from sliding forward and between the stairs.