If you do acquire a mono cartridge and ancillary gear, I advise you to use the mono switch on your preamp, as well, when playing mono LPs.
That's completely unnecessary with a true mono cartridge. It will make no difference since the channels are already summed (which is all the mono switch does anyway). All you are doing is adding in circuitry that isn't needed. If you think it sounds better, maybe it's just noise shaping on your phono-stage from the mono switch that you happen to like.

