Tibetan spaniels are not actually spaniels - they are related to Asian breeds like pekes and shih tzu
As far as the others go, there is quite a variety in temperament among spaniels when you go from companion bred types (like Cavs and American cockers) to the dogs bred for hunting. A boykin is going to be very different to live with vs a cav, though the sweet spaniel temperament will be there.
I think out of the spaniels, a pet/show bred English cocker would be pretty similar in temperament to a Cav.
For non-spaniels, I agree with the coton and havanese. What about a lhasa apso? The ones I've met were super sweet, mellow, and velcro little dogs.