Regarding the ceiling height: 2.50m is not a big deal. Due to the closed construction, it is actually less noticeable. But I wouldn't be persuaded just because of the staircase. 2.60 is simply nicer. :P
I don’t find the original floor plan that bad under the given conditions. However, the staircase is really poorly designed on the edge. Since it enforces the ceiling height of 2.50, it is actually already too short and the space still isn’t enough.
You might do better with a straight staircase. Here’s a sketch. You could also swap the bedroom and bathroom – depending on preference. (How important is this T?) However, the window in the hallway upstairs would then disappear if I don’t want to shorten the dressing room considerably.
