Yes Ammo is right if you get to Douglas in the early hours you can kip in the passenger lounge.
Then I'm told if you want a good breakfast early,
walk out of the front sea terminal, take a left
go past the other Steam Packet office to the mini
roundabout, take the right, you should have the bus station on your left and 'the Caff' is the first shop on the right, there is a car park next to it, only a couple of minutes walk and I believe
they are open 6 or 7am, can check if I remember !