Good for you for signing up for dance classes!
Gym exercise machines bore me, too.
What about a mini tramp you can have in your home? You can bounce around on it while watching tv or youtube videos, and it’s easy on the joints. You can do several ten minutes intervals during the day, which shouldn’t be too onerous, and, while you are bouncing, speed up and slow down. That could help you get used to moving around more, and make it easier to progress to more vigorous activity later.
Swimming is great, as are water exercise classes, for protecting your joints. Walking in nature, observing the world around you, is great. Maybe there are some trails near you you’ll discover with a bit more research. The walks to the store and back are a good start, and, as your body starts to enjoy and then crave exercise, they may become longer.
My motivation? When I was young, because it felt so good – I get the classic runner’s high pretty quickly from both aerobic exercise and from moderate weight lifting. Now that I’m older, I want to prevent diabetes, which runs in my family, and the nasty complications it causes.
Just writing this response is motivating me to leave the computer, put on some long johns and boots, and go walk in the new snow.
Good luck!