I know the feeling! I am almost done insulating my garage. I had done the walls a few years ago, but the ceiling was uninsulated. I decided to use the attic portion of my garage for storage and figured as long as I was putting plywood down in the attic, I might as well throw some insulation down. Not a fun job! But it should retain heat a whole lot better. Unfortunately, the rafters in my garage are just 2x4s, so I could only put in R19 insulation. This also meant I had to use wall insulation and cut it to fit. But R19 should be a lot better than nothing.
Sounds like a good garage !
mine doesn't have a ceiling, but just this very thin plastic sheet has made a huge difference. I still needs access up there to to stuff in storage so this isn't a bad compromise