How to kill dustmites containing in air and on bed?

my child is allegic to dustmite.he is mostly itchy and disturbed at night time.I wash his bedlinen every week in hot water,vaccum the bed,use protector for his mattress and pillow case and try to keep home clean,we changed carpet to timber so that he might get better.but he doesn't seem as getting better.so I was thinking of something that can be used to kill dust mites from air and from bed with some home made tips.do someone knows anything about it plz plz plz suggest me.Iwill be great thank full to those people.I'll also try if someone got any other ideas.thank you.