Since the regulations are very strict regarding light/space ratio, and it would be a shame to create spaces that lack light or simply can’t meet the standards, the idea is to create an apartment with one double bedroom and one spacious area that can be split into two depending on the needs of a potential buyer.
Two spaces would be dividable with a set of panels with a harmonica mechanism. The area in front of the entry would serve as a kitchen + living + dining area and the other side of this space could be used as a bedroom, library, office, or as an extension of the living room area. This way in terms of regulations, you get one room that meets the standards of light/surface ratio, but actually it can be used as two separate rooms.
Existing kitchen would be transformed into studio, existing bathroom would remain within the same walls. New bathroom is formed near the existing one so that the plumbing work shouldn’t be complicated.
This way with minimum demolition and new construction, an old apartment is transformed into a rather spacious and flexible apartment.