Go to a real office furniture company and get good chairs. don't go to Walmart, Officemax, Staples, etc. Back in 1995 I spent $600 to buy a heavy duty 24/7 office manager's chair. It came with a 12 year warranty. The chair is still in use.
I'd also suggest a comfy cot/lazy-boy/ez chair. I'm assuming there are multiple people on duty all the time. This allows one at a time to take a break away from the monitors.
You should make sure everyone can take a 10 minute break out of every hour to rest their eyes.