Matelda
I lost 20 pounds at the age of 74 and came down to a size 12. I did it with the aid of the Zoe nutrition plan - all the principles are free online if you don't want to pay for a personalised assessment (which I did). I utterly changed the way that I eat so that my diet is now mostly beans and lentils, vegetables and fruit, nuts, seeds and grains. My weight has remained effortlessly steady for 18 months, I never feel hungry, am bouncing with energy and hardly get any problems with my osteoarthritis. I walk every day and drag my shopping trolley home from town, but otherwise don't do any fancy exercise. Truly, I am what I eat.
Totally second what you wrote about the Zoe programme, Matelda, I didn't need to lose much weight but I've lost inches of my hips and thighs and agree about never being hungry and feeling full of energy.
I'm 71 and have regained fitness over several years since a knee injury by walking, swimming and cycling. I used an app called Google Fit which is quite basic but does step counts and I find it helps to see my distance increase.
I was also bought a smartwatch for my birthday. It's a Huawei one that cost about £40, again I love how you can see a measure of how much you are walking, standing and moving plus measure many more exercises and things such as heart rate and sleep.
I was a regular gym goer, using the cross trainer and recumbent bicycle but it's not very well maintained at the moment so I do my own thing.
Classes help with having company and inspiration but do keep going and you'll suddenly notice that a hill that was previously difficult is now easy, that's a great moment!