I’d focus mostly on hip mobility/flexibility, as the hip is the area that’s most affected by sitting for too long. Just look up “best hip mobility stretches”. Also, I’d pay attention to your back and find some stretches for it, too. I personally do that every day. I also walk 1 - 2 miles almost daily after work. That’s another very good thing for your body. You need a lot of mobility. I also hit the gym 4 days a week.