I focused on the essentials that you described - creating separate space for office work, enlarging living room space, creating two comfortable bathrooms with essentials in them and, of course, a walk-in closet. There are some suggestions form the design point of view too:
- The entrance area could be more separated from living and kitchen spaces by turning the closet to the side and providing semi-closed space with wooden detail form the kitchen side. This way the entrance is still quite large and comfortable, but this way you are not walking straight into the living area with wet shoes, etc.
- I suggest creating continuity from entrance area to the kitchen by using the same tile design in a very smooth and natural curve, that provides some interesting character to the space.
- Another idea - the office space could have a glass door and a window going up to the ceiling in the same inner wall, that way framing the wall with glass - creating focal point from the living area, as well as providing more daylight throughout the apartment. It would be possible to make the glass semi-transparent from one side or suggest some curtains from office side to provide privacy when needed.

Overall, I feel like this space is very nice and can be planned in many different ways, but I tried to stick to the original plan as much as possible, this way there will be less problems with plumbing, electricity and other things, already provided for you by the builder.