This coming update is going to change a large portion of Minecraft and it's gameplay. With this copper is going to be added. It seems to not be integrated in a good way as of now. Just seems to be shoved on with no real use. I have some ideas to fix that. None are adding tool sets for copper, I think that is not needed and not useful for balance. One thing to note is that spawning of ores and general mining gameplay will change dramatically so this balance could change easily over time.
1) (and main idea)
Adding copper to older recipes to help integrate it and make it more useful. I don't mean going back all the way and changing every one of them one by one but more choose some newer ones to add copper to in a seamless way. One example i had for that was the blast furnace, maybe a copper ingot on the top or bottom along with the iron. Maybe the smithing table, or the barrel. Just some examples, i think staying to newer ones will help make it more balanced and not change too much. I don't think having a copper variant of everything will help either, but adding copper to certain recipes could.
Make it so you can mend iron tools using copper. This will be done in the same way as upgrading Diamond tools to Netherite. A good way to implement this would be to make it so that when you do it it takes away a portion of the damage/life from the iron tool(maybe change color slightly?) and you can only do it once to keep it balanced.
I think copper is a good idea it just doesn't have many uses or reasons to mine it. Even using the spyglass as much as I do messing around in survival.