I think you need to clean up all the dust with your canister vac. I would also buy one or two ionising air purifiers which are very good for collecting fine particles, as small as pollen. Look on ebay. The Lloyds or Flixonase branded ones are what we use, often available for £10 or less and enough for a room. They are almost silent and usually last a couple of years, you can take out the filter to wash it, but when you first use them, dust falls out of the air and forms a ring on the table or wall around the device.
and have reasonably low humidity especially in the bedroom.
You can probably buy an inexpensive humidity meter in a hardware/gardening equipment shop. Some people use them in greenhouses.
Have a few of those disposable dust masks with the plastic valve on the snout handy, just in case he is affected by dust.