I used to break a lot of strings too, mainly the A string, at the bridge. I tried lightly sanding the saddles. Eventually, the problem went away. I don't know whether it was the sanding of the saddles, or gradual change in playing style, or even a change in string type. I just can't remember. I'm thinking the problem went away before I changed string type; and I'm inclined to believe that sanding the saddles did fix the problem.