Whoops . . . Sorry the mic is in the way of my left hand. No matter, this video is all about the RIGHT hand anyhow.
A concept from my Fingerpicking Book 1 from Detroit Folk Workshop. Consider the thumb movement of the alternating bass the same as you would a chord strum. Assign bass notes and patterns to root based fingerings and that's all you need beyond the chord symbol to put a bass line under a melody. Simple? Not really. Straight Forward? Absolutely!!