I highly recommend that you get a 4x to 10x jewelers loupe, or strong magnifying glass. Here is one that I like a lot: second item on page 74.
http://www.surplusshed.com/catalog/ss_catalog_s06_w.pdf
You can inspect the underside of the leaves on all your plants to see which ones the mites like, and only have to treat these, tho I think that flat mites, the type you undoubtedly have, are a lot less picky about the plants they attack than spider mites. The good news is that they are bigger than spider mites and easier to see. But when you can actually see the bugs, it gives you a much better idea of the job ahead of you in getting rid of them.