Vortex Sound Research

I'm recording a song that's based around guitars — kind of a lo-fi indie/alt sound. I managed to play the guitar, but I don't have/play bass. Does anyone have advice for finding a good synth bass sound (doesn't have to sound like an electric bass, but has to fill that spot/frequency range in the song), or writing a synth bass part that fits with a more electric-guitar-type song? Any examples of bands that do this well?

I'm having trouble finding something that really fits. The bass either seems to stand out too much or has no definition/presence whatsoever. And I feel like if I play it at the same octave as a bass guitar, it feels like it doesn't sound deep enough.

Thanks!