I've recently fallen in love with the Hog Island Boa. It's a dwarf boa that gets about as long as as a BP. They're really cool and I love the two that I have.
Another cool snake is the rainbow boa, also a smaller boa, and it looks really cool. I plan on getting one of these soon.
Kenyan Sand Boas are cool and stay really small, I have an adult male is about 18 inches.
You could also get another BP, can't go wrong there.
Out of all of those options, I think the Hog Island Boa would be the one I recommend the most. They are just an amazing boa and they don't get big.![]()