I have been a fingerstyle bass player for the couple of decades, only using a pick when playing guitar but I have recently been using a pick on bass to vary my technique.
I have tried picks of various shapes, materials and thicknesses but my favourites by far are Jim Dunlop Prime Tone 1.5mm small triangle. These are available with or without a textured grip pattern, however I prefer the ones without this.
The material these are made of is Ultex which is Dunlop’s name for Ultem, an amorphous thermoplastic polyetherimide (PEI) resin. This has high strength and stiffness and is resistant to wear. Each pick has hand-burnished beveled edges to provide a quick release.