Hello Bobby,
I do 12-16 hours desk work & the 1st thing you need to learn is to take frequent breaks I take 5 mins break at 30 mins each, i also do stretching while sitting at the desk, bcoz i suffered from RSI. streaching I follow is
1. lift 1 hand then another hand reach as high as possible while sitting, same can be done standing.
2. turn ur neck gently to left & try touching your chin to left shoulder, then to right shoulder.
3. I keep a rubber ball which I press to release strain.
I wont mention all exercise as many of them has to be followed correctly else you may injure yourself unknowingly.
In the morning i do yoga & stretching for the whole body 15-20 mins, its quite difficult to tell about the exercise without visuals, I had hired a yoga teacher for 2 months who made my schedule now which I follow.
Exercise includes the whole body stretching/ jumping/skipping rope/ light weight lifting (light dumbles 1kg) & playing badminton in the evening then brisk walking with larger steps & breathing techniques which now keep me fit.
I have suffered badly in past with acute RSI in my legs/lower +upper back/right hand/neck & even eyes but now I strictly follow breaks every 30 mins.
At my desk i keep things away from me purposely such as pen/paper/phone etc, so every now & then i will have to stand up or push myself to reach out to get the things that itself helps a lot bcoz you will be exercising doing all that, I also changed from soft back support chair to a hard stool, that helps me sitting straight which will make me take more frequent break bcoz I don't have support at my back. Some days i again take the old chair then switch back to the stool later.
I removed the TV from my bedroom so all i can now do is watch tv in the dinning area sitting straight on the chair.
In the car I have now fitted a back lumbar support, which helps me a lot in driving i am thinking to switch to automatic gear car this year which will help me drive without strain in bumper to bumper traffic.
Remember you can replace your computer/car but not your body so consider it precious & take good care.
Goodluck
Ranjan