[davnicwil]

The only purpose of money is to trade work and the captured value of work with other people, therefore it is by definition always someone else's business what you do with your money.

But I know what you mean, you don't want non-directly-involved third parties to know about transactions you make. But then there are always contracts, laws and regulations you must follow and be held to account on. These are the things which bind the economy together and make modern civilisation work.

Your bank balance and the things you buy with your money do not exist in a vacuum. There will always be a trail of your spending left behind anyway, even if it's just asking the people you bought things from what you bought and when. It's an inescapable fact deeply embedded into the nature of what money is, and the function it serves in society.