I had tried sewing buttons on when we were first married. It seemed like a simple thing but they would always come off for some reason. I did a search on the internet and found out that there has to be some slack in the threads so it can manuver into button hole without stressing out the button and threads during the proccess as well as while it's being worn. So the way I accomplish this, is by simply putting a toothpick between the button and the pants. Unlike the darning, this uses a double strand of thread with a knot at the end.
When I'm done weaving the threads through the holes, I remove the toothpick and wrap the thread around the threads where the toothpick was creating a shaft. Then, I bring the needle and thread back down through the fabric and tie off. It's a simple change that has made all the difference in how well the buttons stay on. Now, 2 more buttons to go on other clothes before I am done with replacing buttons for the moment.