I'm not sure if this will help or not, but I quit using 1mm leather cord for the reasons you just listed.
It just wasn't as durable as the thicker cords. Crimping actually seems to weaken the leather at that point, and the leather would soon break through.
It might work better to just glue. Super glue is the best adhesive to use with leather, thanks and a hat tip to Trisha Leary and 'The Old Man' (her hubby, a longtime leather worker) for that advice.

Hook-and-eye clasps are problematic, too. If the necklace isn't "heavy" enough, the hook can come undone. Since the 1mm leather cord will wear out more quickly if there IS weight on the necklace, using both is sort of a lose-lose proposition.
You could try another source for your leather, since it's POSSIBLE the leather you're using isn't a high-quality leather. But I found it didn't really matter, it still broke easily. After repairing about a dozen necklaces in one season, I quit using it.
I hope someone else has ideas, because I DO like how it looks. But now I only use it to lash things to thicker leather cords.
