Get a standing desk sit for 20 minutes then stand for 10 minutes, alternate.
Consider a treadmill at your standing desk, amble 1mph, lose weight and get fitter.
Choose a chair that provides support for your lower back.
Try to maintain an angle of 110 degrees between your trunk and thigh when sitting, keep your knees below your hips.
Adjust your work surface height and your chair to assume a comfortable and natural body posture, sit square try not to lean to one side, it is bad to cross your legs at the level of your knee.
Get up often even for short breaks.
Consider a treadmill at your standing desk, amble while working.