I seem to be very dependent on attitude indicator to check my level of bank and VSI to check if im level - I believe this is bad habit picked up from years of Flight Sim!
MSFS is probably the problem as you say, I know from my own experience that while it is good for practicing instrument stuff it's not great for practicing visual flying. Similar to what Tinstaafl mentioned what my instructor simply did was perform two turns, one in each direction and got me to memorise the visual picture of the aircraft's attitude relative to the horizon. Hold that picture visually and you won't significantly climb or descend.