Options: These really depend on your budget
Redo the staircase in the garage. Maybe a small addition to the garage will allow for a safer staircase.
Install an elevator in the garage.
Put a covered walkway to the garage.
Addition, probably most expensive, and most disruptive.
She-Shed, still have to go outside during the winter. Plumbing and wiring will need to be supplied, plus hook up to sewer/septic.