I often sit at a desk all day and all evening. I find that these things help:
Good chair. Height adjusted for my keyboard/mouse height. Upright back. Lumbar support. Comfortable-but-supportive seat.
Good posture (when I remember to pay attention to it).
Split, tented keyboard. Mechanical switches that don’t require too much pressure.
Good display. IPS panel. Light anti-glare surface. Backlight that actually dims the light source, either without pulse-width modulation, or with PWM at such high frequency that it cannot induce flicker fatigue. Brightness turned down much lower than the default. Calibrated at that brightness setting, optionally to a slightly warm color temperature.
Muted room lighting. Nothing behind me bright enough to reflect much on the screen.
Comfortable clothes.
Cup of water. Regular trips to the kitchen to keep it filled.
Frequent short breaks. Start the laundry. Get a snack. Look at objects outside. Wash a dish. Bring in the mail. Make the bed.
Exercise. At least 10 minutes daily; preferably 30 minutes or more. Stretches. Squats. Rhythm games that require full-body movement.
Have you considered making a Linux virtual machine now, and learning small things a few minutes at a time between other tasks? That ought to give you a head start when it comes time to commit.
But you’ve made a lot of assumptions in your comment, and you’re mistaken about most of them.
I played the side quests. Many came with a good backstory, but that is not gameplay. Nearly all were copy/paste instances from a small pool of tedious tasks. There were a few memorable exceptions, but very few.
I explored the world, as much as one can “explore” something that is fully labeled with point-of-interest markers. They lead the player to a repetitive handful of uninspired encounters, cloned over and over again.
It has plenty of other flaws as well. If you loved it, then I’m happy for you, but I found the gameplay boring.
The strengths I found in The Witcher 3 were its story, lore, characters, and Gwent. Not its gameplay.
Meanwhile, Gwent is a surprisingly well-designed strategy game. So much so that it ended up spun off into a stand-alone version (although I don’t know how good the spinoff is).