It seems like most of the larger dogs have the tendancy to be couch potatoes, like great danes, with the exception of my cousin's dane, that dog is extremely active!

Like some have said already, I say go for some of the older shelter dogs.

Or go for a pug/rat terrier!! All mine EVER does is lay around all day sleeping, right now he is sharing my chair, snoring like he hasn't slept in weeks. But that's just probably his own personality, I don't know what others of his mix would be like.

Good luck on your search