You'd probably have to get advice from others who break strings. I have done so few in 30+ years of playing that I am sure they were flukes or string defects, or installation screw-ups. Bend it too hard over the bridge when you're installing the string and you can fatigue the core. It's only a matter of time from there. What is your playing style, and, when you break a string, where does it fail?
I would wonder, for those of you who break them, what are you using? Are heavy strings more durable because of the size, or maybe less durable because you have to stretch them tighter to get them to pitch? Flatwounds are usually a bit heftier for a given thickness, but often less flexible. Which is more important? I would think that the most flexible strings would be the most resilient, but I don't know.