Many big dogs are gentle giants. For example, the Leonberger (although they have a short lifespan) and most other big dogs. Small dogs have a reputation for being hyperactive and yappy. If you do decide on a big dog, don't get a guard dog like a a Doberman or pit bull, as those can tend to have a more aggressive nature. But every dog has a different personality, so it's improtant that you meet them personally so you can understand their temperament.
Boykin spaniels! They are adorable and so friendly. Mine is older, so he doesn't do much. Some have a little extra energy, though, when they are a puppy, but they tend to calm down. They also like the water. :)