The idea is minimum destruction and reconstruction but still can manage to have a well-used spaces.
1. Add one toilet near existing one, re-arrange the existing toilet more efficient with a bathtub and stand shower, bidet and sink. Washing machine can be putting here.
2. Demolish the wall at entrance to have more space with shoe cabinet at foyer and a larger kitchen nearby.
3. Re-arrange the living room area, dining table and have small reading area for work and entertainment.