Maybe a small male red tail would work - but there is no telling if you end up with a male that will get larger than 6 feet - I know someone who had a male that was probably around 40 pounds or so - not sure about the length of that one!

Kenyan sand boas, Rosy boas, Rainbow boas - those all stay pretty small - some smaller than others.

Rosy boas and Kenyan sand boas are both very easy to keep - rainbow boas have some strict humidity requirements I think but I have not kept one.

They should be just as easy to feed as a ball python - my boas actually are easier to feed than my BPs - all on f/t too.