Thanks for your reply Zarah. :)
I have tiled floors in the kitchen, bathroom and hallway, but carpet in the lounge and bedrooms. On the vet's advice, my boy is now banned from the main bedroom (he used to sleep in there) and I try to keep him out of the other carpeted rooms unless I am spending some time there. I have considered wooden floors but good ones are expensive and to be honest, I'm concerned they would be slippy and not very cosy!
Like you, I hoover a lot, including the furniture once a week, and dust (like you, not an expert in that! :D) with a damp cloth. Try to keep the place well aired too to avoid moist, damp conditions which the little blighters thrive in.

Just wondered about the air purifiers as I saw one recently in B&Q but there seems to be a bewildering range of them available in general and don't want to splash out on one if they're not going to make a huge difference.
My vet isn't a big fan of immunotherapy - she reckons they aren't seeing the success levels with it that the suppliers claim. Do you feel it has made much difference with your dog?