Help with SP3T relay (on-off-on)
and i guess solid state may harm the quality

Overcome your fixations here. I'm (also) a guitarist (and music producer) and have recorded probably about 100 of my own songs and, it wouldn't bother me one bit to use solid state switching and dump mechanical relays straight into the garbage. I've also mastered about 500 other songs hence, I have some knowledge in this area that is meaningful.
So, forget about mechanical relays (you'd have to use sealed reed relays anyway to avoid contact oxidation issues) and use analogue multiplexers to do the guitar signal routing. Of course, the devil is in the detail and some will work better than others but, given that this question is fairly open-ended, I can only generalize on the technology.
Using analogue switches will mean battery consumption is in the low mA range (as opposed to relays that will have a high tens of mA consumption).
If analogue switch circuits can be engineered to accurately multiplex microvolt level thermocouple sensors into a common amplifier chain then, there's absolutely no reason why the same ideas can't be used for millivolt level signals from guitar pick-ups. It's a no-brainer for me.