Playing left hand bass is the way to go. But another possibility, especially since you also play guitar, is to play foot bass - same concept as left hand, but the keys are a lot bigger. As an organist first, I still play foot bass and left hand bass. It's great when you're playing piano and can play a string bass with yyour feet.

I just so happen to be considering putting my MidiStep pedals up for auction. You'd also need a basic sound generator (MIDI'd up to the pedals). If you're interested, drop me a line.