Get a second henhouse built, treat with Creosote (inside too, especially perches, and any nooks, corners etc) let it dry, then treat the hens again and move them in. Then paint the old coop with Creosote too. Use the old type Creosote, you can still get it from fencing supplies.
We also use plastic nestboxes, just get storage boxes from the supermarket, cut a hole into the front and put on a roof (better if you can get boxes with roof already fitting). the pop into the henhouse. Easily removed, cleaned, disinfected etc. We use some of the waste hay from the goats as nesting material in them.
No mites since we started to do it that way, in our first year we tried all the super new products with absolutely NO success whatsoever.