Here’s a simple, cool idea.
Start on the 5th fret of E string with the first finger of your fretting hand.
Be prepared to play the 7th fret of the A string and the 7th fret of the D string.
(the fifth and the octave of your low note (A) if that helps)
Decide on a two-bar rhythm that’s comfortable and PERFECTLY playable with your right hand.
Whole notes (one per bar) Half Notes (two per bar) Quarter Notes (4 per bar, like a walking bass line) or Eighth Notes (8 per bar).
Play two bars on the E string.
Then shift to play the 7th fret of the A string - same rhythm.
The idea is to have a simple move for your fretting hand, and focus everything on your plucking hand and trying to move your thumb from the pickup (when you strike the E string) to the E string (when you strike the A string)
Then do this exact thing again, but go from E string to A string to D string, moving the thumb anchor each time.
Go super slow.
I’d love to make a video for this, but I don’t have the time currently.
Hope this helps! Holler with any questions.