not to go against the tide here,
, but i use my thumb to pluck, along with my index, middle and ring fingers - like classical guitar technique. makes playing octaves and string skipping a lot easier. also makes the transition from fingerstyle to slap a lot more fluid - i go back and forth sometimes in the space of a few beats. takes dynamic control, but sounds cool.
the secret is to not plant any fingers anywhere. when not in use i rest my thumb on one of my lower strings. planting fingers, imo, is a very inefficient way to set up your plucking hand. a lot of energy and hand strength is wasted when fingers are planted - keeps your hand stiff, which is bad, slows the plucking hand down.
if anything needs to be planted, i plant my arm on the edge of the bass.