Dont Forget
Also mention this to the airline when you book your ticket as it may be some assistance to be seated near the toilet.
Consider also climbing stairs.. are you okay with that or do you need time?? You might need to pre-board as the ATR has a stair door.
If the A320 is on a remote stand e.g. one without an aerobridge you may need to seek assistance with a passenger lift or 'DPL' this is a movable platform that is put up against the stairs and lifts you up as there is a few stairs to climb on the A3-- aircraft.