Dust Allergy - Keeping humidity below 50% to kill dust mites?

[Arpegios]

DC has a dust allergy which is basically caused by dust mite poo. I've been reading that dust mites thrive in damp conditions, so bought a humidity meter for their room and it basically doesn't go below 70%.
Unfortunately it's a North facing room that gets no sunlight in the winter.

I believe we need to keep it permanently below 50 to control the mites. I put our big loud dehumidifier in the room and that worked - but is not really sustainable long term.

Is this only answer a dehumidifier of some kind? Can you get ones that are, quieter and designed to run 24/7? Any other options?

Many thanks

I have a mecco which has a quieter night mode. Normally you want to aim for between 50 to 60% humdity so 70% is high. I only ever run it during the day to lower humdity and for drying washing. This is more than enough for me to keep it at 50%.

Is the room heated properly?
I have asthma and dust mite allergy.
Bedding changed at least once a week including mattress cover. Vacuum the mattress weekly and the carpet daily.
A dry atmosphere makes my asthma worse but fundamentally humidity is curable by heating.

If humidity is 70% in the bedroom it will most likely be the same in other rooms too and probably get higher in the colder months. Look at PIV units online, Although more expensive than a dehumidifier to buy, It runs 24/7 and will sort out the humidity of the whole house. It’s also cheaper to run so will be more cost effective in the long term

Keeping it under 50% can help, but it’s not always easy to maintain, especially in winter or cooler rooms. A quieter dehumidifier or better airflow can help, but it usually works best alongside other changes rather than on its own.