Boa Constrictor Amarali is another that can stay on the small side.

They are a little more demanding of husbandry while young, but they have Suri looks in a small package!

I recommend the book 'Complete Boa Constrictor' which discusses various locality boas and species, and I would also recommend the website for Rio Bravo Reptiles for researching localities.

My Amarali came from Barry Miller, who is a wonderful resource over the phone if you have any questions about BCAs, and of course a great source of quality captive bred BCAs.
He usually has lots of pics on his site as well, but less husbandry info than Rio Bravo.

Good Luck!