I’m with Barbara on this. I started out on a lap harp that only went down to the F below middle C, and I had to transpose the bass line ALOT. As long as you stay within the chord, it should sound fine. For example, if your bass line is Low C-Low E , and G, you could invert the chord to G, Middle C, & E. Or just play everything an octave higher. How high does your lap harp go? Mine only went to F, and this was a problem too.
I tried re-stringing my lap harp to get the low “C” and it didn’t work. Even with a thicker gauge string in order to get that note I had to adjust the tension too low. Was like plucking a piece of spaghetti, and did not sound good at all.