Insulate garage ceiling
Option A - Blow it in (if there's no insulation in place between ceiling and floor now.) Drill holes, stuff in hoses (or hire a professional insulation-blowing company who may be better at it that you will be - it's somewhat tricky.)
Option B - rip it open, insulate, re-cover. Consider adding radiant floor heat tubing first.
Option C - add sheet insulation, and more drywall over that. You do NOT want exposed plastic insulation on the ceiling of a garage that's below living space - that would constitute a huge fire hazard.