I am not sure if this is historically correct, or has already been taken up, but I know the middle age as a dirty place due to the fact that the ordinary citizens lacked toilettes and generally knowledge about the dangers of living in their own excretion. Shouldnt you see that their living conditions are more or less unhealthy by implementing ulcers in some peoples faces or people throwing buckets containing a yellow liquid out of their windows? Wouldn
t that create a much more realistic atmosphere?
Maybe you could differentiate between rich and poor regions and create one or two castles which are utterly horrible places and should not be travelled through as they feature the danger of coming in contact with a contagious disease like the plaque, moreover these castles could feature a high level of criminality and be exceptionally dangerous for your own health.
You could also introduce a mission to isolate a town in which the plaque has occured.