Hello all,
The follow profile solves it indeed. Thx to @David_Graeff.
So to summarize for one of the items:
I have a knx item called ‘temperatuur_binnen’. This one is linked to the corresponding knx channel in a knx.items file.
I have also setup a MQTT Generic Thing with PaperUI and added a ‘temperatuur_binnen’ channel with just a MQTT command topic:
After that I linked the temperatuur_binnen item to the mqtt channel and selected the system:follow profile:
This way whenever the knx temperature sensor sends a new measurement, the measurement also gets forwarded to the mqtt broker 
Hopefully this helps someone else too.