My solution for this apartment is using the height - adding 2nd level in the middle room and moving floor structure above the kitchen on the same height 2.6m.
Floor structure can be made out of metal and/or wooden beams.
In the middle room there are stairs for the 2nd level and dining area with a big table with six chairs. Space under the stairs is used for built- in shoe storage and wordrobe. I suggest making window on the place where now is hole in the wall and also one window in the upper area. It can also be wall out of glass cubes instead of a classic window.
On the 2nd level there is bedroom, working area and walk-in closet in the space above the kitchen ( heigt of the room is only 185cm ). A hole in the wall or vault must be made for the closet.
In the living room there is total 5m height and visible vault with fresco or some other color for the vault. There are modern pieces of furniture, lamp and chandelier and giant plant.
In the drawings I suggested some models and brends of the furniture and the lightings.
Modern lines of furniture and lighting, meating vault ceiling and doors and there will be light!