We have several threads about exercise: cycling, running, swimming ......
Browse round. Make notes. Brisk regular walking is good for bone health. Don't forget too that housework counts as exercise as does gardening. Lifting the ironing board, taking laundry up/down stairs, making bread ......... weeding and tidying in the garden also counts as well as getting fresh air.
Put cycling for example into the search box? When I needed to tone up I borrowed a puppy, it took 14 months of almost daily walking to get back to feeling comfy. I would never join a gym - too organised. On my 50th birthday I joined the swimming group, I never went after that day