As far as appearance and maybe a little spice, Brazilian Rainbow Boas might be worth looking into. I'm not so sure about their display potential (I've never set any of mine up in a proper display enclosure), though. Fun species, though the morphs (the albinos, anyway) apparently still have some bugs to be worked out of them.
Though I've not kept these, it sounds like what you're after is a Green Tree Python. My understanding is that seeking out pathogen tested USCBB specimens directly from a conscientious breeder is worth the effort, and that's absolutely the way I'd go if I got into them.