My biggest boons was adding a tuneable LED strip along the back side of my desk, which softly lights up the wall behind my monitors, and getting a Colorimeter.
The colorimeter in particular has been great - most monitors come eye-searingly bright out of the box, and with a white point nowhere near optimal - I calibrate all three of my displays (MBP + 2 LG 4K 27" monitors) to 6500k, 120cd/m2 which for me is tolerable and leaves my eyes not feeling so tired at the end of the day.
The colorimeter in particular has been great - most monitors come eye-searingly bright out of the box, and with a white point nowhere near optimal - I calibrate all three of my displays (MBP + 2 LG 4K 27" monitors) to 6500k, 120cd/m2 which for me is tolerable and leaves my eyes not feeling so tired at the end of the day.