Do I need an air purifier, better ventilation, or both?

Air purifiers aren’t very common where I live, so I’m still trying to understand what they actually solve.

My bedroom gets dusty, but the bigger issue is how stale it feels when the windows stay closed. Opening them helps pretty quickly, but then I’m dealing with pollen and traffic noise.

I’ve been looking at models from Levoit and Coway for the dust side of things. One option I found outside the purifier category was cozeware freshflow, a window-mounted fresh air system meant to bring in filtered outdoor air without permanent installation…

Now I’m wondering whether I need a purifier, better ventilation, or some combination of the two.

Would it make more sense to start with an air quality or CO2 monitor before buying either one?