We went with Therapy Dogs International, just because that's who the school goes through. I plan on going to nursing homes. My MIL was in one and the people there didn't seem to respond to people, but they had a resident cat, and everyone would perk up when she walked by.
I think Yorkies are perfect for this because they're non-allergenic, and can fit on someone's lap, or get picked up to say hello. And we tell Snoopy he makes the world a better place just be being in it!