What are some inherently gentle breeds? Not very excitable or highly energetic. A dog that seems to know when he/she needs to be gentle.
The gentlest dog I've ever known was a Bearded Collie - she could be very energetic and excitable, but she was always beautifully calm when someone was sick or frail. She was also an adult dog when I got her, and I believe she considered me - and most humans - to be puppies in need of looking after. Which is why I think a grown, female dog of the smaller herding and sporting breeds would be the best bet for finding a gentle dog.
Not to start WWIII, but many varieties of dogs have drawbacks in terms of gentle. Terriers are so feisty - they're vibrating the whole time they're sleeping, and like many working breeds, when they spot something awry they WANT TO ADDRESS THAT ISSUE RIGHT NOW. Not very relaxing. Large dogs have a reputation for calm and gentle personalities, but I think they are just too freaking heavy - when a dog is over 45lbs, their physicality is unavoidably strong. The tiny breeds, while they can be demons, have a much-deserved reputation for being excellent lap dogs. Still, if I was looking for a dog to do therapy work with, I'd start looking for a female dog about 3 years old, 35lbs or less, who was a spaniel or collie mix.