TL;DR
Put this in your ~/.xsession:
setxkbmap -option caps:escape,lv3:ralt_alt
Reset with:
setxkbmap -option
Caps Lock
A pointless key, it’s better to have it be Escape instead:
setxkbmap -option caps:escape
AltGr
Repurpose it to Alt so you can switch workspaces with one hand:
setxkbmap -option lv3:ralt_alt
Documentation
There is none, you can look at these options listed here:
cat /usr/share/X11/xkb/rules/base.lst
Stare at them for a few hours, try some out, and you might stumble upon something useful.