When you have to mix thick cookie batter or something similar by hand, the counter top is usually too high to do this comfortably. Instead, place a washcloth or dishtowel into the kitchen sink and place your mixing bowl on that. The sink is usually at least 7 inches lower than the counter top, which makes it a good height for mixing without hurting your shoulders (or elbows) as much.
I’ve been using this method for quite a while. Just yesterday I mixed a thick cookie batter this way and it works very well for me. Try it and let me know what you think!