Still uncomfortable?!
You have made all the right adjustments and yet, you're still not sitting comfortably? Get a backrest and a footrest!
A LITTLE TRICK...
If you work continuously at a screen, take a 5-10 minute break every hour if you can. Leave your workstation, move around, stretch!
And if your office chair still doesn't feel right ... Then there is only one radical solution left: change your chair. :)