Recently I have found out about decentralised MVHR’s, i wonder if these are a good idea, but they seem costly per each unit.
Dehumidifiers seem to be always out of stock at the moment.
I recommend MVHRs. They not only remove humidity but also give fresh air, while recovering the heat in the exhaust air. There is a discussion of suitable models on another thread.
These are some devices I have discovered.
Prana versions
These are costly, using a ceramic heat recuperator
How do I find a suitable installer in my area?
In the above linked thread this comes out a winner
I suggest you skip down the thread and find someone who can advise about fitting, although my understanding is that once the right size hole has been cut through your wall any electrician can fit one.