"back button" for previous document

That’s not really how the binder and editor (plural, don’t forget) relationship is designed to work. You can read up on it in these prior discussions if you wish to know more about why.

If it’s becoming a problem in knowing where you are, maybe the small amount of space used by the header bar is worth leaving it enabled? That way you also get a read-out of your history by right-clicking on the buttons, rather than strictly the blind movement you get with the shortcuts. Otherwise the inspector is also a place that prints the name of the thing you’re editing, up in the “card” at the top.

There is only one command I think that absolutely requires the header bar to be visible, and that is the path menu. You can use Opt-Cmd-R to Reveal in Binder at any time, or if you prefer menus, it’s in the View menu too.