Best way to go about netherite upgrades?

I was making a custom type of weapons for one of my packs and realized that I can't do netherite upgrades like in vanilla because my custom weapon (which is based on a diamond sword) and a normal diamond sword would just use the same recipe. I thought about using an unobtainable item as the diamond weapon, but then I realized I'd have to recode the durability system myself. What's the best way of doing this?