That's your idea of short?
Croc, I would hate to disappoint you, but that really was a rhetorical question. (trollface). Thanks for the story anyway, thought it's a bit naive and incorrect, but it describes the main things pretty well.
Now, I'll try to cover what's missing in your story.
You were right when you said that people started to use promissory notes as the prototype of paper money. You were right when you covered where inflation comes from.
Everything is correct, but just one thing. The situation you've described has nothing to do with the principles the modern banking system works on). Before the middle of XX century, the powers used paper money simply because they were more convenient than carrying a heavy bag of gold with you, BUT if you really needed, you could ALWAYS exchange your paper money for a FIXED amount of gold (or any other value which was used to secure the paper). This was stamped on any banknote of every state. That stood for reason and helped to avoid the inflation.
Even in your story, every paper (or legal obligation) used for a payment was backed up with something. Something fixed. That tailor knew exactly what was the price for that dress and when he exchanged that paper for gold coins he willingly accepted the discount. It was his choice. Feel the difference with the present situation - money are just paper and nobody guarantees you that tomorrow they will be worth something useful.
When I say about golden currency I don't actually suggest that people deal again with real golden coins and/or bars. You can still use paper or even electronic money, but they must have a FIXED value. FIXED, something that cannot be changed in time and there must be a free acceptance of the discount. If the market situation changes, it's not money which should be depreciated, but goods and services instead. That's the idea.
P.S. And a final side note - in Middle Ages, usury was considered morally wrong, it was a state crime as well as a religious sin.