Plants, for sure. And, if you have pets, the spider plant is safe.

https://www.countryliving.com/uk/wellbeing/a668/houseplants-to-purify-house-air/

We run several Germ Guardian HEPA purifiers with ultraviolet light for viruses. I have been pleased in general, though one of our small wall units failed this week in a splendid electrical stink. It was 5+ years old. Our big floor units have been excellent. Honeywell is generally outstanding, too.

I also think that HEPA offers quality air purifiers, besides, you can find a list of the best air purifiers on Google and choose one of them. You know that it's important to keep the house clean, but there is another invisible part that requires special attention, it's the air. Using an air purifier helps you make sure that the air you breathe is clean, but not all purifiers work the same, so there are air purifier reviews that help you choose the best one that is right for you. Well, I read a lot of descriptions and reviews of air purifiers before making an order and I recommend you do the same.

Some good info here: https://seetheair.wordpress.com

I've used four different brands: Austin Air, Coway, Winix, and Vornado.

The Austin Air is a powerhouse. It is shaped like a small ottoman or stool, somewhat industrial looking. The filter media contains various metals. I have the "plus" model filter which captures VOC's and can really handle some awful air quality situations. It is liveable amounts of noise on medium, and a loud low sound when on high. The air flow out of the unit is unidirectional and it might not work in the particular spot in the room where you prefer. Austin units are $500 or more. The filters are also pricey but last a long time. However this is the type of unit you need if you have heavily polluted air. The reason is the filtration media. It is a substantial unit. It is American made out of one factory in New York State. They offer excellent customer service as well.

Coway and Winix are similar products. Both are good. Initial cost is low at $150-$250. You have to plan for filter replacement every 3-6 months at about $50 per replacement. Easy to maintain and live with. Some models have louder fans than others. Some models send clean air straight up, and others blow clean air out on a 45 degree or 30 degree angle. That's not adjustable, so you have to make your choice about your preference and then you're stuck with it. Read the Amazon reviews carefully, and you will find a model that you like.

I picked up two round Vornado Cylo units because they were deeply discounted right before the holidays. So far, I love them. I have one in each corner of my studio apartment to take care of stagnant air flow. One is near the head of the bed and one is near the sofa. Because they're new, I don't know how soon I will need to change filters - the company suggests 6 months. The purchase price was about $110 each and the replacement filters are about $25. Best bargain out of all the different brands I've tried. So far I think both of these are working very effectively.

My mom currently has my old Coway and Winix. They are a good fit for her home, but in my studio they were not the right fit for my space. In my studio I have an Austin which sits on the floor, and I wheel it out to the center of the room if its really a bad air day. I have the two Vornados in corners of the room. Most days I have the Austin on low or medium, and the Vornado's on low. Occasionally I'll need to turn the Austin on high for about an hour, then I can turn it back down.

Honeywell is a good value, too. It's very basic, just a cabinet and a filter. You can't go wrong with those, as long as you are sure you are buying a True HEPA. Unfortunately in the whole industry, "HEPA" does not mean the same as "True HEPA." Look for "True HEPA", or, read through all the specs to see how it has been tested and certified.