Boas would be a good start. They'd give you a feel for handling bigger snakes, but they don't get as massive as others. They also come in a lot of beautiful colors.

On the columbrid side, why not take a look at Indigo snakes? They get fairly long (longer than some boas), but aren't as heavy bodied, and even in the wild are pretty docile. They do have strong jaws, though, since their way of killing their prey includes grabbing the head and crushing it. They're gorgeous animals, and you can probably find captive bred youngsters.