Possibly moving house in the summer which will mean kissing goodbye to our garage gym which has come together so nicely over the years

... but it's not all bad as the new house has an integral double garage so about 2x as much room

. Anybody on here got an integral garage and tried to do anything to insulate it? I'm trying to figure out what would be best to do to go a bit further than I did in our current one (single skin detached garage, where I essentially just put down stall mats and slapped some white paint on the walls, and a few celotex boards on the rearside of the garage door) - because that thing was blood freezing/baking at the different times of year... Not sure we want to fully commit to a total garage conversion with planning permission etc. but only just starting to think about it. Any ideas?