Hi Pippo,
This is short description of my project. I wrote it so you can understand as best as possible what is my idea about the apartment.
By standards toilet should be near entrance, so I place it there. I know that chimney takes up a lot of space but I decided to put the bathroom on this side because of pmubings, so the plumbings of both apartments have the same vertical for pipes. Bathroom is not large but is very fucntional. It contains all needed elements: toilet shell with cistern inside the wall, corner sink for saving space, a shower with glass door and washing machine. Loft is small so it doesn't have enough space for separate laundry room. I didn't know if you need a water heater so I didn'r drove it, but if you do need it, it's place is above washer. Bathroom doors are "pocket" doors, they are similar to sliding doors, but "pocket" door goes into the wall as you can see in project. It's also space-saver.
Kitchen is next to the bathroom and also have the same vertical for the pipes (by standards). You said that the apartment is for one or two people, so I made bar for eating. Kitchen have all needed elements like stove, fridge, sink and enough space for dishes. I planed one shelf instead of storage room so the space could be more open.
Bar is complex and in one side is for eating, on the other is TV shelf. Bar is also boundary between kitchen and livingroom. Livingroom is spacious and it has three-seater with bottom drawers for storage and coffee table. I didn't want to burden space with furniture so the livingroom doesn't seem cramped and overcrawded. I imagined for sitting three-seater and space in bay window with pillows. My recommendation is that you hire someone to make you custom furniture with dimensions that suit this appartment. The most of furniture are designed by me, because I couldn,t find anything that looks like I imagined it. I sent you pictures with furniture similar to mine, so you can have the best vision.
Stairs are made of combined shelves so they are useful and don't take much of space. Working area is within the stairs-shelves, and have desk and chair for work. There is enough space for books, computer, papers and other work material.
Mezzanine is placed above the kitchen area on hight of 2.3m. As you wished for, it's used as sleeping area with sofa bed, shelf for TV and stereo, next to sofa bed is cadenza for clothes with lamp for reading on it. Railing around the mezzanine is made of glass , and that makes space more visually open. During the day, most of space should be very brigh because of bay-window, but during the night there is adjustable home lighting all over the place.
I hope my english is understandable, best regards!