28.18Bass should sing

Don't think:

“my left hand is just a metronome.”

A good bass line can have melodic logic.

Try:

C → B → A → G → F → E → D → G

with corresponding harmonies:

C → G/B → Am → Em/G → F → C/E → Dm → G

You've already used this progression in pop.

Now play it with bossa rhythm.

The style changes completely.