Dear client,
Very often, simplest approaches often turn out to be the most appropriate and economical.
Main difficulty: Giving suitable height to the mezzanine floor without compromising the livable heights required in the rest of the house.

To solve this, one has to identify the human functions that do not require much height. They are:
1) Sitting.
2) Accessing objects at eye level or below.
3) Storage.

If we were to accommodate these three functions under the desired mezzanine floor, a height of 2.2 meters can be achieved for the mezzanine without having to lower the ground floor level or any other civil changes.

The specifics of these three functions would be:
1) Sitting---------------------------------------------------Sofa seating for the living room.
2) Accessing objects at eye level or below-------Standing space in front of the bedroom wardrobe.
3) Storage--------------------------------------------------Storage cabinets for the living room and Wardrobe for the bedroom.

Further, the doors / windows can be created under the existing high windows. Existing bathroom can be retained but made a little longer. The passage provides space for storage and for main electrical board, heating control etc.