A smaller boa... A male Bci (common boa constrictor) might be a good choice. They should stay 6' or smaller (for males if fed properly), are generally outgoing and curious, calm, and easy to handle if you work with them. They have high food drive, so hook training is a must to let them know that food isn't coming when you want to handle them. Semi-arboreal, so they stay in their hide sometimes and will also use branches to climb. a 4' x 2' x 18" pvc cage (or similarly sized tub) is required for adults. I own two and love them. Both of mine were easy to handle even the first day I got them. If you do go this route though, perhaps get the snake at a show or from a local breeder so that you can handle it in person and test its temperament. The central American boas (and some of the smaller localities like hog islands) can be more nippy and defensive, so again, handling in person will help. In your case, a male Bci, even a morph like a hypo, albino, etc. would probably be a good bet. Morphs vary in cost, so you would need to explore your options and find a boas that you really like the looks of.

Another good choice might be a kingsnake... About 4' and most calm down with handling and as they grow. They are out more in the daytime and more active than BPs. I do not own one personally, so can't give you personal experience, but I've heard many people love cal kings and black Mexican kingsnakes.