I started with air filtration in the mid '70s by building a filter wall. I was attempting to mitigate ammonia fumes wafting from a small commercial blueprint machine. The machine had an adequate filter but volumes of fumes came from the finished prints making an entire floor of our office building uninhabitable. The filter wall was the last of several failed attempts beginning with a commercial filter. Fast forward ten years and we bought thee Honeywell Environcaire HEPA filter units for our house. A two filter system, a HEPA filter resembling an oversized ring style engine intake filter and an activated charcoal wrap around pad that covered the outer ring of the HEPA. They sit typically on the floor and a fan draws air in through the pad and HEPA, out into the room. This style is efficient and adequate for anybodies lungs. By definition HEPA appliances filter 100% of microbes including viruses.
I had to put filters to the ultimate test in 1999. I designed, built and patented a robotic chromosome dissection system. Any DNA floating into the system could contaminate a tiny piece of a chromosome. Periodically I sampled the surfaces and air. In a years time of continuous operation, it was clean. When you are selecting a product, you want to look at the noise level when operating. My Honeywell units were great on low but the two higher settings had to be shouted over. Check the availability and cost of the filters. If they have it patented they could be almost as expensive as the whole unit. HEPA filters are replaced either yearly or two years. The carbon wrap varies from 3 months to 6 months. If Honeywell still makes Environcaire units, take a look at them as a jumping off point. Sears may carry them. Systems can get expensive fast. I found features to be worthless. Currently I have a FilterQueen Defender on low, right by my bed. It is raised, placed on top of a dead Environcaire. This is neither an endorsement nor indictment. For the value I liked the Environcaire, the FilterQueen is great but I didn't catch, there's always a catch, was the purchasing schedule for the filters must be kept in order to keep the lifetme warranty in effect.
If you have forced air HVAC, consider the electrostatic filter and UV units. I have them and they are good with AC but less so heating. I developed a total efficiency UV sterilizer for National Jewish about 30 years ago. It took an extra power hookup to the building to drive the powerful UV lamps. Although I still bought a house unit, by looking, my guess is it only catches a fraction of microbes.
If you still need more, please PM me.