I don’t walk more than an hour a day and that’s just to the shops and back.

That's plenty for upkeep, your body knows that walking is a thing that it's supposed to do, and continue to do, and not just an interim state between sitting at a desk and sitting in a car which can be safely deprioritised just as it deprioritises balancing on one leg while holding on to a cabinet leaning over a mine-field of legos to get hold of the winter bedsheets stowed away in a far-away corner.

If you want to up the ante a bit add hanging to the walking: No need to get into pull-ups, at least not intensively so, just hanging provides enough data to the feedback loops in your shoulders/upper back to prevent getting confused as to how they're supposed to control the muscles there.

And if you're in a bad state (or just enjoy it), say you're fat and walking is actually a joint issue: Swimming. No need to train lap times, just enjoy yourself, of course, if you enjoy training lap times then do that.

While I'm at it last but not least: With every exercise, don't choose the hard stuff. If you can't do 10 pushups then you shouldn't be doing pushups, you should be training to get to 100 wall-pushups: Less resistance means you can focus on form and actually develop good form, and many repetitions of a low-resistance exercise tire the muscles just as fewer repetitions of a high-resistance one. Muscles will become stronger in the recuperation period after the lactose starts burning, as such don't set a number goal but train to exhaustion.

Oh, and this guy.