There are at least 2 paper filters that are a fit in your "pancake" air filter housing:
Wix 42373 and Fram CA77.
I would take the "expert" assertions that they restrict air flow with a huge dose of skepticism. In the real world they work great and no dust gets through them. The color is bright white and as dust accumulates the color of the filter exterior changes giving you a clear indication that it's working. The inside remains bright white.
