Just start really, really slow in the beginning, and keep to a pace that is comfortable for you. And it's good that you have a sense of humour!!!
You tube has a ton of yoga videos, including beginner. Maybe spend an hour looking at them, and bookmarking ones that you think you might be able to try. I've a bad back from an accident, and whenever I did yoga and found a pose hurting my back, I'd do Child's Pose until they moved on to a new pose.
Pilates is another form of exercise that you might enjoy. For me it is reminiscent of yoga - very small, controlled movements that are extremely low impact.
Good luck :)
The best exercise in the world is to bend down and help someone up.
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