Had a Marcus from IKEA for years, switched out to a Herman Miller Embody and I can sit in it for hours without any butt or back pain. I do wish I had a headrest on the Embody but its not the end of the world.
The HM range is expensive but with the 12 year warranty they're well worth the cost compared to cheap ones you'll likely replace.
+1 for github, ive used the project and discussion features before and they integrate nicely. You can join it all together with pull requests as well.