There's a very friendly large poodle that gets walked near where I live. They always come over to greet me while I'm reading or sketching. The owner's sweet about it. The mastiffs I remember were military dogs. Depending on where you were, you could come down for coffee in the morning, and then realize at the end of the meeting that your feet are warm because you've got a dog snoozing on each foot.
What instruments do you play? I know that Basch - someone who's important to me - he's been doing coloring with his brother. Crayons and books and all that. The idea is that it's good fine motor control for his hands, and calming. Something they can do together that's pretty low stakes.