A desk does not require one perfect posture that must be held all day. Your back usually responds better when a comfortable supported position is combined with regular changes, short standing breaks and simple movement throughout the workday.
Place the screen near eye level, keep frequently used items within easy reach and allow your feet to rest securely. Every thirty to forty-five minutes, change position, walk briefly or complete a few relaxed movements instead of waiting for stiffness to become painful.
Posture is only one part of a healthy back. Gradual strength work, regular activity and adequate recovery improve how well your body tolerates sitting. Persistent pain, leg symptoms or increasing weakness should be assessed by a qualified healthcare professional.