What about a grey hound rescue?? These are the most gentle dogs you will ever meet. They can stay inside and they just lounge around all day. My aunt rescued one and they are such gentle giants! As your grandson gets older, I'm sure that he would appreciate more of a "manly" dog, if you know what I mean. If not a grey hound, then I vote for a beagle, or a pug! Pugs are small and great dogs.