I would not plan the toilet upstairs separately from the bathroom. It is often the case that you are standing half-naked in the bathroom, just about to shower or having just showered, applying lotion, etc., and then need to go to the toilet... and then? For example, the children have friends visiting, you cannot walk half-naked through the hallway and are out of luck. With small children, you don’t have these "problems" yet, but later friends also visit late in the evening. For this reason, we also have a children's bathroom because we wanted our own bathroom that can be used without having to go out into the hallway.
Best regards Sabine