Ionizers are pointless. Fun devices, with their gentle buzzing, but useless.
Humidifiers are pretty useless unless you have a super-efficient house with almost no draughts (unlikely in the UK). The weather here rarely gets very dry.
'purifiers' just sound pointless, particularly if you have a regular (draughty) UK house. Imagine the effect of the unit you might be thinking of Vs the volume of air in the house and moving through the house.
You might have done this already, but keep a journal of your symptoms and the conditions around you. Record the environmental conditions: weather, house conditions, cleaning regimen.
After a while look at any correlation between the environmental conditions and your health. Remember correlation is not cause but then look at the things that you think might have an effect on you. Think about taking action on those.
You could consider a N95 or smaller mask??
As a hayfever sufferer, consider the antigens you might be in contact with: pollens, fine particles (dust, animal dander etc), flour...
I've had rhinitis-like symptoms now & again. They're usually resolved by taking things away like animals, fabrics or even doing some cleaning (well, getting others to clean). They've never been resolved by adding things like 'ions', airborne water or voodoo science.
