I don't think the draft is that bad. The sticking point is, indeed, the staircase. You have to walk around the entire staircase to get to the sleeping area. Personally, it wouldn't bother me. In the basement, I find the ratio of children's room to hallway space unsuccessful. Also, that the staircase intrudes into the children's room. Has this detail already been resolved? I find the kitchen with a 3m block and wall space sufficient. I like that you are not building upwards, but instead incorporating the slope into the design, we solved it similarly. However, I would have concerns about the construction costs, I just say slope, right now it's just brutal!!!!