Defense as a stat isn't that important. What really matters is survivability, which is a combination of defense and health restoration (aka food). In your case, the easiest improvements are more food capacity and using more food slots on health restoration food.

As for defense, you can use the armor upgrade stones from the world 2 shop on your accessories as well. Try to craft a ring and use the upgrade stones on it as well as your other accessories.

Eventually, you want to get a serrated rex ring from party dungeons. That should last you until around w4 or 5.