This person has the right idea but I would really recommend getting a 4" filter and putting it on the back. This will allow for more air flow which is important for removing dust.

If you want to kick it up a level I use a Corsi-Rosenthal box in my house. Modified design with 3 two inch Merv 13 filters. Merv 13 will filter out viruses and pet dander.

Here is the design https://engineering.ucdavis.edu/news/science-action-how-build-corsi-rosenthal-box and you can find a lot of Youtube videos on how to build them and some testing them https://youtu.be/lbWiZSsEqPg.

I recommend getting a decent fan instead of a cheap one as it should be able to pull more air through the filters.