Watch where the bathroom door is facing. If it is facing a relatively unused space, then don't worry about it. If it is facing the living room, or perhaps the bedroom door, then consider covering the doorway with a curtain or hanging. The cats can get through below. Your current solution sounds fine for most siuations too. It becomes a matter of aesthetics. If you are absolutely determined to do it to the letter, then maybe a cat-flap kind of set-up could work.
