It is important to work on Posture, Balance, Strength, and Flexibility to remain functionally fit. Sometimes you can combine poses to work on two or all of these at the same time.
When you are sitting in a chair, try sitting straight without using the back of the chair. That will help you to develop upper body strength. Cross your ankle over your opposite knee for a nice outer thigh and hip stretch. Cross at the ankle if crossing above the knee is not good for you.
Try standing and repeating the same movement to incorporate balance and strengthening of the hip, knee, and ankle joint.