I also love retics, but they are quite the opposite of a burm. They like to move, alot! They can be friendly with regular handling, but they like to move, alot! I own a dwarf that is just over a year old, he can be nippy at times, but he likes to move, alot! I have personally handled a 12' that was like handling a HUGE corn snake!
I would say if you want something modestly large, a well fed colombian red tail boa female can get close to (or beyond) 10'. They are cheap and easy to come by. They are usually super tame with minimal handling and they don't move much when they are out.
Also, if you really wanted a burm, you could call it a retic when it came time to move to another state!