I wouldn't recommend a short-tailed python until you have more experience, as they are more of a challenging snake to keep and handle, and should be left to intermediate keepers.
Have you considered a rosy boa or sandboa? Both are cool snake... I am partial to rosies, they are definitely one of my favourites and very underrated.
Some BCI such as Crawl Cays stay under 6' as adults as well.
You could always go with a cornsnake too, I personally am not a big fan of them, but many people do like them.
There are also Spotted and Children's Pythons, Garter and Ribbon snakes, and many different subspecies of ratsnake to choose from as well