Charecteristics of the Preferred Location

Danger Lad! has been asking to sleep in my room a lot lately, for vague and not very convincing reasons. Last night, he asked to sleep in my room again, and I said okay (as I fairly regularly do, since I fairly regularly don't sleep there myself), and I asked him, again, why he wants to sleep in my room instead of his.

My room is comfier and cozier, he says.

This is plausible. I've had way more time to make my room exactly the way I want it than he has. What makes it comfier and cozier?

The bookshelves. Danger Lad! wants a big bookshelf full of books for kids. Also, he would like my toy Mini Cooper. That would be very cozy.