Flying when really fat - impossible without buying 2 seats?

[FknOmniShambles]

I last flew about 5 years ago when I went to Iceland and was a size 22. It was a squeeze to be comfy in the seat but I used a belt extender which was fine. Sadly, I'm now bigger (please don't judge cos I say it all to myself every day anyway) and am about a size 26. My weight is around my belly and bum.
Fiance is desperate to get away, and I'd love to as well. I've told him I'm scared of flying and we have explored rail trips and cruises... But ultimately we are limiting ourselves and I feel so bad as its my fault.
Any ladies of a similar size have any tips about plus size travel? I'd be very grateful!
I will book two seats happily if that's the only option.

I'm not exactly huge but a size 16/18 and I always have an aisle seat and quite often don't sit next to my H who likes window seats - we always pay the extra and get emergency exits too . It won't make your seat bigger admittedly- but I do think you feel less squashed in - I would def say aim for an aisle seat if a bit bigger.