The 5:2 is the only thing that works for me these days. It’s a healthy way of life as well - it certainly lowered my blood pressure, as well as my weight. It’s not as difficult as you might think, as you always have a “normal” day to look forward to, and you don’t have to spend the five non-fast days counting calories. I try to stick to 600 calories on my fast days, though as you say you can go up to 800. I have all my calories in an evening meal, which works better for me than small meals throughout the day. Exercise is important, though, both for weight loss and for health. I can recommend the Fabulous Fifties routines on YouTube - they start at 10/15 minutes so you can combine a few or just do one, in the comfort of your own home. I appreciate you have to take care if you have back problems though.
I hope you enjoy your trip - how lovely to have something to look forward to and work towards!