Here are some hints that will help you achieve better posture & reduce back pain”.
Exercise regularly to keep abdominal muscles strong. This helps support the spine. Avoid carrying heavy items to one side (example a heavy bag worn over a shoulder). Always bend at the knees, not the back, and quickly drop the load if it's too heavy. When standing your feet should be shoulder width apart. Use a lumbar roll or back support to support the lower back. Maintain an arch. Leave your computer screen every 20 minutes and stretch and stroll for a minute.

Cross ankles rather than knees when sitting. Don't tighten up muscles when in the straight posture. Relax into it. Sit with back against chair, and knees in line with your hips. At desk, arms should be flexed at a 70 to 90 degree angle to elbows. Walk tall. Think of pulling the entire body upwards towards the sky.