I believe a PCX can be all you need. The latest model is highway legal (and capable IMO). It's small enough to let you go and park anywhere and you can't beat it for practicality. It's okay 2 up and has some of the best gas mileage around.
Now when I came back from Hawaii (my wife stayed behind for a couple of months) all I had was a GROM for several months. If I could only have one vehicle and it had to be a 2 wheeled vehicle, it would be a GROM. Not my Trail, not a regular size motorcycle, not a scooter.