If you want to lose weight you need to accept that you have got to change your eating habits, not just while you are dieting, but for the rest of your life.
The main mistake people make is spending the time when they are dieting longing to return to the eating habits that made them fat in the first place. You will not lose weight just by exercising.
So I suggest plan ahead for a new eating pattern to go with your new life as a retiree. The eating pattern always being recommended is the Mediterranean diet, not a dietbut an eating pattern. Best summarised by an American food writer as Eat food, not too much, mainly plants. and its corollory
If it came from a plant, eat it; if it was made in a plant, don't. 'Plant' being, of course, the US word for factory.
Here is a link to a good site describing it www.bbc.co.uk/food/articles/mediterranean_diet
As for exercise, as everyone says, walking is good. I also do Tai Chi, less energetic than pilates, which I used to do, but as theblate Michael Moseley showed, just as good and effective as more energetic forms of exercise.