I can only make suggestions, it’s up to you whether to claim DRE or not.
The rules are clear though. If you have assessed needs (after a Needs Assessment) and you have to buy certain items which are disability related you may be able to reclaim the cost, depending on the financial situation of the disabled person.
You buy the goods, send in the receipt, and get refunded.
Perhaps you have already seen the British Lung Foundation pages on indoor air pollution Your home and your lungs | Asthma + Lung UK but I’ll post a link here in case it helps anyone else. They don’t recommend brands but do give hints on alternative ways to clean and what to avoid.