These are some of the tools I use when sitting (sedentary) at the computer.
Google Chrome Extensions > PostureMinder (https://chrome.google.com/webstore/detail/postureminder/dkmkfopiihabelocpelofchappjjnpkm?hl=en) – reminds me to stop slouching and stretch continually. Not in an annoying way either, and its free.
EyeLeo – reminds me to take breaks and also do eye stretches at intervals that you set. Its free, can be a little intrusive…but I think thats me just getting annoyed at having to do the exercises haha. EyeLeo.com
another good eye one is Save My Eyes > https://chrome.google.com/webstore/detail/save-my-eyes/mbhpdkldehghoilbopkcpfijdhnincmh?hl=en
F.Lux – cuts out the blue light filter on my computer screen so I can naturally go to sleep on time and not be kept awake by the blue light in the screen that effects your ***.
Lumbar Support – I use them in the car and also on my chairs. You can find them cheap on ebay.