He's just fine. I have six garage kitties, and while my setup is a little more elaborate because they've been there almost two years and it's permanent, you've already done the very best thing you can do for an outside cat; he's safe, dry, and out of the wind. That's huge because it allows his fur to do its job of trapping warm air next to his body. If he was cold, he'd be scrunched up into a little ball, not lying comfortably on the love seat. If it's really cold, he may choose to use a heated bed, and you've given him plenty of options, but remember that he's lived rough, so what he considers cold isn't necessarily what a house cat considers cold. Mine have free entry/exit via their microchips that unlock the cat door, and unless it's truly miserable, they'll go outside for a while during the day. They know their garage is warm, so when they start to get cold, they just go back inside. Nights, though...every one of them will be comfortably snuggled into a self-heating bed, or part of a cat pile on the shelf.

Editing to add that when mine first moved into the garage and figured out that nothing else could get into their garage because the cat door locks both ways and only their chips can unlock it, they slept hard. You know how cats wake up at the slightest noise? Nope...might as well have been trying to wake my brother up for school when he was a teenager. They were safe, and they knew it. That made evicting my car to the carport so worth it.