Sitting for how long? How about working in sets? Work for 30 minutes, then walk around or do something else for 10 minutes?
You could arrange it however you like, and then after doing that for two hours, you take a 30 minute break.
Could this be worth a try?
Also, I snack while working. I used to eat candy, but I switched to healthier snacks. My favorite is mango slices haha
How about music? Do you play any music while trading?