Dear Client,
Here is my interior design proposal for your apartment.
FLOOR PLAN  
To achieve new, functional space, all interior walls were demolished. The entrance to the apartment is closed in an entrance hall with a built-in closet. That way you will not enter the apartment directly, bumping into living space from the outside. The new living area consists of a living room, dining room and a kitchen. Home office zone is placed in the living room close to the entry. The challenge with this apartment was how to use the central space of it as it doesn't have access to natural light. So I placed a laundry room and a master's bedroom walk-in closet in the central space of the apartment floor plan.
In Option 1 of the floor plan, in the laundry room are placed separate washing and drying machines. In Option 2, washing and drying machines are placed in a built-in toilet near a small toilet. I proposed Option 2 in case the water sewage system for the washing machine can not be placed so far from the existing sewage system which was originally placed where the small toilet is now.
In the kitchen, there is a kitchen island in the middle of the room with a stove and kitchen hub above it. Kitchen island can also serve as a small 'bar' or 'breakfast area'. The kitchen can be divided from the dining room with frosted glass sliding doors. The laundry room defines spaces in the living area and separates the night area from it. 
Two bedrooms have a shared bathroom with a shower, double washbasin, toilet and a bidet. Each of the bedrooms has a sofa, closet and a desk as essential pieces of furniture.
The master bedroom is a separate area with its own bathroom and walk-in closet. Walk-in closed fills the central area of the apartment as it is a space which doesn't need natural light. There are no doors between the master bedroom and the master bathroom in my proposal, but for example, a sliding door can be easily placed in if necessary. Also, there are no doors between the master bathroom and the walk-in closet. Main focus when entering the master bathroom is the large shower with frosted glass wall. Besides a large shower, the master bathroom has a toilet and a bidet and a double washbasin. The small existing area in the upper left corner of the plan belongs to the master bedroom and serves as another walk-in closet.
There are built-in closets in the hallway in front of the two bedrooms.
CEILING PLAN 
All ceilings in the apartment are lowered 30 cm so that they can hide the ventilation and cooling units. There are openings in the ceiling closed to the windows so that curtain rail tracks can be hidden. Also there are 'boxes' in the ceiling in the living room area and the kitchen which contain downlighters. 
HEATING, COOLING AND VENTILATION.
For the heating, I kept all existing positions for radiators, which are going to be just replaced for new ones and covered with radiator masks. Regarding the floor heating, in some standard floor heating solution, the whole floor should be raised, which then causes the need for shortening the doors and making a 'step' in balcony door thresholds towards balconies, so I chose the option with radiators.
For the cooling and ventilation system, as an architect, I suggested the central units hidden in the ceiling. Exact type, size and number of the units and ventilation grills built in the ceiling should be considered with an HVAC engineer. 
Thank you and I hope that you will like my proposal!