Well, found what I need...
Fission Bass Powerchord FX Pedal
I had one of those for a while, did not care for the tone at all.
There are a couple of different routes you can go. One would be to sit down with the band, face up to the fact that you're a trio, and pick music that you can pull off as a trio and sound great rather than pick songs that need parts you don't have. Thinking in terms of arrangements can also help; sometimes stripping a song
back actually helps, rather that trying to fill it up
more. When I was in a classic rock trio, we did a WAY slowed-down version of "Can't You See" that entailed letting whole notes hang in the air forever. People loved it. And also, being in a trio can just give you space to stretch out with your own playing.
The other route would be to fill in with technology. I would argue you actually need several pedals. An octave by itself gives you a thicker sound, which helps some, but it generally just winds up sounding like heavier, fuzzier bass. Using a pitch-shifter to add a fifth up is more what you want, but if it's a fifth up from your bass note it's still way down in low end territory and can leave you with a muddy bottom-heavy sound as a band. You want to have an octave up, to get you into guitar frequencies, and then a fifth ABOVE that.
My solution was to bi-amp, a "Royal Blood" setup. I run my bass into a MicroPOG, which has both dry and wet out. The dry out goes through my bass pedals to a bass amp. I set the MicroPOG's knobs to be 100% octave up and nothing else, and the wet signal then goes to an EHX PitchFork (and if you're going to start with just one pedal to build from, get the PitchFork). That's set for a 5th up and 50/50 blend. With all the pitch-shifting, by this time the affected tone pretty much sounds like a kazoo, so finally that signal runs through either a fuzz (mine is a SUF Civil War) or an EHX B9 Organ pedal, depending on the song, and then off to a guitar amp (just a Blues Jr.). That's a lot of setup, but it finally let me be able to fill space as much as I wanted in songs that needed it while the guitar was off soloing.