Bigger holes = less purity But to answer your question, a mesh coffee filter will do, they're like $2-$5 at any grocery store
Do you believe there is any significant amount left over after it has been filtered through a paper coffee filter? Because I certainly do.
You can run the same batch a couple times. I usually make 2-3 batches with the same trimmings/bud. Shake it, strain it through the coffee filter, and repeat 2-3 times.
I just used two strainers one on top of the other. Im not worried about a bit of greenishness. mainly about the plant matter. i mixed it in a jar for no more than 15 seconds at a time. i repeated 3 - 4 times using two cups of frozen chopped bud and 32 ozs of iso.