Commercial buildings have all sorts of rules under Ashrae in the US. Generally in commercial there is a minimum air exchange rate for occupied space. Pre covid it was being constricted for "green" energy initiatives in the name of energy and $$ savings. That restriction was allowed to be really clamped down on (more savings) if certain conditions were met like CO2 monitoring or people counters, both more tightly targeting how much fresh air people actually need and minimizing waste in conditioning outside air that isn't necessary. Post covid a lot of that got thrown out, commercial buildings are now generally over shooting OA exchange in the name of not turning these spaces into germ breeding grounds.
None of this really exists in the residential sector, but maybe it should. Homes in even the recent past are "leaky" enough to get enough outside air exchange for the low occupancy rates without actively conditioning and bringing in outside air. Some modern energy efficient homes that are wrapped and sealed extremely well might pose an issue to this.
By all means get a decent sensor that reads CO2, CO, PM1, PM2.5, and VOC. Radon if you are in a risk area. Your regular thermostat probably already gets you temp and humidity. It needs to have some way to do long term data logging, five or ten minute sample rate for a year for example. You really want to see how things are different across seasons.
With that data in hand there are plenty of things you can do if you need to introduce more OA to occupied spaces. Generally there are heat exchangers that can be dedicated to that sort of thing. Or a simple motorized damper opening up a small filtered OA duct on the intake side of the air handling unit. Ideally those devices would only be activated on unacceptably high bad air quality readings.