When we refurbished our entire house we installed single room heat recovery extractors in both the main bathroom and the ensuite. There were all sorts of reasons why we did not know for a full MVHR, which was certainly right for us.
We went with this model:
which is one with a humidity detector and hence will up the power if the humidity goes over a certain level (which you can alter easily).
I have to say they have been universally excellent and I thoroughly recommend them.