The solution is simple : I left the preparation for the stairs and in that site I put a closet.
The bathroom is lined up in a way that does not have problems with drain column.
On the ground floor the main space has two black semitransparent sliding doors that divide the reception and the bathroom from the bedroom and kitchen.
The first floor is a little bigger : in the reception area takes place the kitchen so you can have more space for the bedroom and livingroom.
Hope you like the idea .
Thank you