When I was a child in elementary school a friend of mine and I would walk two St. Bernards after school. They belonged to her neighbors and they were happy to have us give them some exercise. I remember them as being smart and very gentle. The site below may answer some of your questions on this breed. Good luck with your selection. You are going about it the right way.

http://www.dogbreedinfo.com/saintbernard.htm