Posture is a HUGE factor in neck / upper back pain. Make sure to sit up straight but comfortably throughout the day. Make sure your screen is at about eye level and preferably straight in front of you. An EXCELLENT exercise for the neck is chin tucks where you pretend to make a double chin and you should feel a stretch in your upper neck just below the base of your skull. This should be done 20x each hour. This is easy to make a habit by doing 20 with each bathroom break, 20 at each meal, etc. Use a lumbar support if possible & experiment with where it feels best. You can roll up a towel and put it at your lower back to safe money. While sitting up with good posture, hold your arms in a "W" shape with elbows bent and squeeze your shoulder blades together. Stay out of a range that makes pain worse and this should help you a lot.
It is very much preferred to avoid crunches or motions that involve a slouched position of the back as this is the most likely cause of your upper back and neck pain in the first place. There are plenty of ways to work abs without crunches. Good luck.