If I had dust mites, I would do the following:
Tear out the carpet and replace with hard flooring. If that were not an option, I would spray mite killer on the carpet and vacuum vacuum vacuum.
Vacuum all the furniture and drapes.
Dust everything from the fan, window ledges, all furniture. Everything.
Run a HEPA filter.
Lower the temperature in the room. Mites don't like cold.
Clean the room. Again. And again. Until they are gone.