Now, I always try to get an aisle seat because I can sort of 'twist' a little if I need a bit more room
I only needed an extender on a Virgin Atlantic flight - my hips used to measure 57 inches - and I could manage every other seatbelt.
I'll tell you one thing - the stress I used to put on myself getting ON the plane was always far worse than any seating problems!!
Remember, most planes have armrests that lift, so do that if necessary - and definitely if you know the person next to you!