My Addison's best friend is an English Mastiff. His name is Fin and hes 140 lbs and still growing
he is just a puppy so he is playful, but he does not have near the energy that the yorkies do.
He is not my dog, he is a friends dog and we get together a few times a month at their ranch and the dogs go nuts together. Fin has never been aggressive to ANYONE, he is a huge baby. I think their temperment has to do with how they are raised.
My only concern is that he will accidently pounce on my babies, they are never left alone unsupervised. The weight difference is scary!