Assuming that you don't want to get into any fun exercises / sports ( I do kayaking, cycling, hiking, climbing for instance), then you need to prioritise some kind of movement. Go out for a walk before work or at lunchtime, then it won't be dark and you get a proper break from sitting. If you're in a call where you are more listening than talking consider doing press ups/sit ups/kettlebell during the call once a day.