If he loves his house and uses a litter tray outside of his house (ie doesn't pee in his house) then it sounds fine for now. It is not essential that they have a large house, although they do build bigger nests when they have a large house. What tends to happen when you give them a large house, is they move their pee corner inside the house as well, to have an ensuite bathroom
So then you need to move the litter tray in the house too.
If you were thinking of giving him a bigger house, would suggest adding it but leaving his existing house - and see if he moves in. If you put bendy bridge tunnel over the door of the new house he will almost certainly move in. They are tempted to go down the tunnel and then find a nice dark space inside that mimics a burrow
So move in.