With the netti pots, I think you can buy sachets that you mix with water - presumably makes a sterile saline solution. I'm sure there will be threads on hear about using them.
Ds is 10, has a few allergies, house dust mite, grass pollen, cats, dogs, horses, peanut and hazelnut. He outgrew egg allergy a few years ago.
Yes, deep clean your room regularly. Get rid of all unnecessary fabric - carpets, curtains. If you do have carpet, when hoovering, go over the same spot 10-15 times. The worst places for dust mites to be are where you stand for dressing. Dead skin will fall off you and your clothes and this is what the mites feed on. Yuk! The experts also recommend moving your furniture to different spots regularly to stop these 'hot spots' from forming.
We have not put down a wooden floor in ds' room yet but I can tell when his room needs a thorough clean by his sneezing and coughing.
I sure if yo repost in the allergy section, others will have more suggestions.