A zipper slider can be replaced if the teeth and tape are still intact. If the teeth are broken or the tape is torn, the whole zipper may need replacement.
Sewing thread should match the fabric type. Lightweight fabric needs finer thread, heavy fabric needs stronger thread, and stretch fabric needs flexible seams.
Fabric pilling is not always caused by poor material quality. Friction, harsh washing, excessive detergent, and high heat can also speed up the process.