If you are going to use modern small bathroom tiles then you must keep in mind some simple rules. The colour scheme for such bathroom should be picked up very carefully, it cannot be against the main colour scheme of the house or apartment.
To ease such process you may just make pictures or photos of the apartment main space and then compare it with chosen bathroom design to be sure they are not contradicting each other.
Having in mind many ideas won’t really help you, as you may get lost in them. It would be better to decide what style you need and then start to add details to it. Since it is going to be small bathroom everything including tiles should be used to visually increase the small space. The most radical solution is of course just break the walls and rebuild the bathroom.