Coinjoin an amount that you know you won't need to sell. Also, it will be a while before exchanges do that, or at least I think so.

Exchanges are slowly adding Lightning support also, and when you deposit with that, you end up with different UTXOs, so that's a way of dealing with coinjoined coins too.

Unless you live in Europe, they aren't trying that hard to track you, they just want to know how much you buy to tax you.

But seriously there are things you gotta be careful about with the uncoinjoined ones. You don't want to spend a small amount of the uncoinjoined from a large UTXO causing that person to know the extent of what you HODL. If you don't know what I'm talking about, read up on that.

Good luck!