I am no professional but air quality as been a pet peeve of mine, here is my advice.
The main problem with air purifier is that they create a false sense of security while doing only part of the job, and in many cases the job can be done better by opening the windows to change the air.
The step number one if you care about your air quality, is getting an air quality monitor. They are quite cheap, and should display temperature, humidity, PM2.5, TVOC (total volatile organic compounds), and CO2.
Then you can treat the problem adequately if you have one.
If your home ventilation was well designed and you live in a non-polluted area the numbers should be OK.
Then you only need an air purifier if you create some kind of dust and/or not ventilate during cooking.
If they aren't : try opening windows a little and experiment to see if you can maintain the number in the correct range throughout the day and year. If you can't you'll probably have to have some form of professional installation to get the ventilation done properly or need to move.
HEPA filters in air purifier, only remove particulates but have no effect on TVOC or CO2. HEPA filters are expensive and need to be changed regularly.
TVOC and CO2 only grow indoor, the only thing you can impact is how fast they grow, and therefore how often you will have to change your air to maintain good enough quality.
To reduce the growth rate of TVOC the first thing to do is track the sources of it and remove them (for example avoid bad paints, glues, remove clutter (the less object surfaces you have the less they emit and use inert surface materials), chemical bottles...), and then make sure that you keep temperature and humidity stable.
To remove CO2, the only way is to have adequate ventilation (either by opening the windows or by mechanical ventilation), (and you can only get as low as the CO2 concentration of the outside air (which is growing...) ).
This ventilation will bring fresh air from the outside. Then it all depends on where you live and the quality, temperature, humidity of the exterior air.
For example if you live in a cold place, opening the windows will lose lot of heat, so you can mitigate this problem by using a ventilation that recover part of the loss heat. If you live in a humid place bringing you probably need some ventilation that dry the air. But the key is to ventilate as little as possible to maintain the number in the good range.
If you live in a place where the quality of the exterior air is bad, you probably should move, but in the mean time you can use an air purifier to mitigate the PM2.5 problem.
If you live in an old place that was designed without ventilation in mind, it will be quite expensive and may create some noise, and you probably should move.