Make sure your enclosure is 110% escape proof. Snakes are escape artists. They will find a way out if there is one. I currently keep a small collection of north american milk snakes, 5 ball pythons, and a few rat snakes. I have had 3 escapes in 15+ years of keeping. One was because of my own stupidity (cage left unlatched), the other two were the same snake from the same cage.....i still don't know how she got out.
As far as recommendations, i would suggest a ball python. They don't get very large (about 4 feet long), they are extremely docile, and they are attractive snakes.
What kind of king snake are you looking at? Some are kind of "jumpy".
I set up most of my snakes on aspen or pine bedding, stay away from cedar....its toxic to snakes...provide some sort of heat gradient (one end of the cage about 10* cooler than the other) and a heavy water dish (snakes are strong and can easily tip a dish over).
Hope that helps, let me know if you have any questions.
