Look into sand boas, but not Kenyans if you want something unique (javelin sand boa), rosy boa locales are awesome, hog nose snakes have really unique personalities and many like to hiss and act "tough" if you will I find it really cute, also there's children's pythons. I think a male would live comfortably in a 20 long. It up to you just research there's tons of options and I'm sure many other subspecies of sand boas that stay small.