Add walking for 2h per day is the recommended I’ve seen.

Thanks, 2h is a bit too much for me, so what I do is about 3-4 10-12 mins walk-sprint walk reps. Basically half walk (3.5m/h) and half sprint-walk (4.4m/h). I wish I could do more but my joints are not really good.

Just walking is better. You get a steady burn. If you do high intensity you burn calories for a good while afterwards. Mild intensity doesnt do much.

    > It's a bit difficult to add more weight lifting because I tended to hurt myself

Did you try slightly lower weight and higher reps? It is worth trying as an experiment. Current scientific literature says that 5-30 reps is the ideal range for gaining muscle mass. And, as you said, the relative heaviness of weights to the person makes a big difference for injury risk.