Your pain is due to muscular stiffness more about the quadriceps that is contributing to patellofemoral pain. Before doing any strengthening exercises, please take steps to reduce the stiffness of that muscle. Do not sit cross legged, take frequent breaks and do stretching exercises.
Next Steps
sitting is going to be an art for you due to your lesser than average height, thin body frame and presuming that you have a desk job.
Health Tips
we can do a teleconsultation if you want me to help you more.