Bass playing doesn't have to be complicated. Why not learn two notes that you can play on (almost) any chord? Then you can apply some cool rhythms and techniques to those two notes and have access to thousands of bass lines!
Welcome to the world of the root and the fifth.
Motown backing track:
Bass Guitar Intervals
If you want to get up to speed with exactly what intervals are and how you can use them in your playing, you might want to take a look at these lessons:
How To Name Intervals On Bass (Plus Application/Tips/Tricks)
Figure Out Bass Lines By Ear – INTERVAL Shapes
Instantly Make Up Beautiful & Melodic Bass Lines! (With Upper Intervals)
For this video lesson, I'm only using two shapes plus an octave (which is exactly the same note as the root). Here they are.

Root (red) up to a fifth

Root down to 5th (the 5th has been put down the octave to get this shape)

Both shapes together
PDF Download. Take the patterns below and move them around the different chords, coming up with different rhythms as you go:
Bass Guitar Patterns
Shapes and patterns on bass are a powerful way of:
- Learning songs and bass lines quicker: Make Up & Memorise Bass Lines REALLY Easily
- Linking a shape to a sound to work on your ear
- Learning new styles authentically: 9 Rhythm and Blues/Soul Bass Patterns
It's part of the study of learning the fretboard inside out. Here are some more lessons that will help in that regard.