My hips are 60+ inches depending on whether I'm at my highest, and I've never had problems fitting in an airline seat. The only times the seat belt was tight was on the smaller planes for short 1-2 hour flights, but I managed to force it closed. The kind of planes they use to fly across the North American continent are bigger, and the seats, even in economy, are roomier, so I'm sure the ones they use to fly across the ocean will have plenty of room.

Yes the toilets are cramped as you go in and out with the door bent in, and the aisles in the economy section suck. I also am fairly tall and long legged so my knees press against the seat except for in the emergency aisle, and if the person in front of me slams their seat back without giving me time to slide my legs down my knees get crushed.

Basically, unless you're the size of an average 13 year old or shell out for first-class, flying is somewhat of a pain for everyone, so don't let it stress you too much.

If you find that you do need a seat belt extender, you can make your way over to the galley (usually there will be a flight attendant there during boarding) and discretely ask them for one.