So I have been using an air-to-water heat pump for three years and am super satisfied.
Costs for heating and hot water 65€ per month / all year round.
Temperature bathroom/living room around 23° total living area approx. 200m²
Noise disturbance? When I stand on the veranda at night and hear the oil burner pump in the neighbor's house start up (through the chimney) it is about as loud as my heat pump. And in summer it hardly runs at all and in winter the windows are closed anyway.
PS: I have forgone the ventilation system - I didn't like it.
And which heat pump did you install?
What house standard regarding insulation? What heating load does your house require?
Why do you open the windows at night??? So that you warm the surrounding air of the house and it does not freeze from outside? That is a reason for a controlled residential ventilation system in new buildings...
a) Still live in a rental apartment
b) despite having controlled residential ventilation, cannot imagine that the air in the bedroom is cool enough (this is, however, a personal assumption)