Wow this issue was really not on my radar. thanks!!

On amazon I can find some CO2 sensor like the one below whose reviews say it is a bit more accurate. What sensor would you recommend? Also in the USA we don't have trickle vents, but I can crack a window. We have an Airmega HEPA filter and it keeps our PM2.5 at about ~5 most of the time thru most of the house, so I think I can crack a window w/o increasing pollution in the house much.

to keep the noise down I am tempted to crack the window in rooms that are adjacent to the bedrooms rather than in the bedrooms themselves. I assume if the intervening doors are open or the house fan is on either way the air is mixing fast enough that this suffices?

What would you advise?