Well, a male hog island boa will likely stay under 6'. I know of some breeder age males that are 4.5'.

There are many, many colubrid species to choose from.. kings, milks, corns, rats, and their morphs. Any particular color(s) or patterns you're interested in?

sand boas (kenyan and roughscaled) are lovely little pets.

jungle carpet pythons stay pretty small..

sumatran short tail python or even a blood python