Best Mobility Exercises for Neck Tension

I have been getting a lot of tension in my neck and shoulders lately which is leading to some nasty headaches. I am looking for the best mobility exercises for neck tension that I can do at my desk or at home. I think my posture is the main culprit and I want to fix it before it becomes a chronic problem.

I have started doing some chin tucks and some side stretches for my neck. I am also trying to strengthen my upper back with some rows and face pulls. I am in the US and I find that I am often clenching my jaw and tensing my neck when I am stressed. I want to find some ways to relax those muscles and improve my range of motion.

Do you have any favorite moves for relieving neck stiffness? I am also wondering if using a specific type of pillow or a heating pad would help. I would love to hear your suggestions for a simple daily routine to keep my neck feeling good. I am ready to get rid of these headaches!