Though the seats of adult chairs are narrow enough to get through doorways, some chairs have brake handles or axles that stick out and gouge trim or doors that open only 90 degrees (like in a bathroom with tub, wall or cabinet that prevents you from opening the door 180 degrees). We had to take one of the kitchen doors off for ease of access (fridge handles prevented opening that kitchen door more than ~80 degrees). It would not hurt to measure the smallest dimension of your tightest doorway before you chair-shop. Note that with a door open 90 degrees, the smallest dimension is not between the jams, it is between the back corner of the open door and the other jam. There are chairs out there that will fit your doorways, you just need to check the design. Some designers must assume everyone lives in assisted living places with extra-wide doorways.

To get the chair in the trolley/bus, you would definitely want a foldable and lighter-weight chair. You're light enough for an aluminum chair.