Worth knowing what changes the answer, since a single number for you is not stable either.
Surface. Rougher road, lower pressure. A route with poor tarmac or gravel sections wants noticeably less than a smooth one.
Weather. Wet roads generally want a little less for grip.
Load. Panniers and a laptop change the total substantially. If you commute loaded and ride unloaded at weekends, those are genuinely different pressures.
Tubeless versus tubes. Tubeless can go lower safely, because you are not going to pinch a tube against the rim. This is most of why tubeless riders quote such low numbers, and it does not transfer to a tubed setup.
Temperature. Pressure rises as tyres warm. Minor, and it exists.
On your specific situation: if you are on 100 psi and getting bounced around, you have room to come down a long way and the ride will improve immediately. Do it gradually so you learn where the limit is rather than overshooting and deciding low pressure is bad.
And if you are on narrow tyres on an older frame, the bigger upgrade is often fitting the widest tyre that fits. More comfort, more grip, no meaningful speed cost on real roads, and it lets you use the lower pressures the rest of us are talking about.