I’m about 280, 6’4 size 46 waist, xxl shirt and am flying United for my Disney trip. Will I be able to fit, do I need an extender for the seat, or will I have to buy a second seat...
FWIW, my husband was able to fit in typical coach seats with a waist size similar to yours, although he carries all his weight in his belly in a frontward direction and not across his hips where seatbelts and armrests would interfere, so I'm sure the "fit" is different for everybody.
I weighed in that neighborhood and the worse I had to do was ask for an extender. Seat belt lengths vary from seat to seat and airline to airline so you may need it or get away without it. I never had to pay for a second seat.