I like playing with a soft synthetic in the mains and a poly in the cross. The opposite of most people, but it feels way better. If you haven't tried it, do it!
I broke a fresh set of strings in under an hour!
Obviously I am having durability problems. I could start watching the ball and hitting the middle of the strings, that might help. But if you don't swing hard enough to break frsh strings with one miss-hit then try syn in the mains and poly in the cross. It is how federer does it...