Bitcoin unfortunately It is not the best means of exchange. I still find it easier to pay something using a credit card. You just swipe your credit/debit card into a machine and type a few digits (password). Bitcoin should be easier than that to be more widespread. Not everybody is tech-savvy.

What about creating a hardware wallet as small (preferably smaller than) a credit card without the need for a smartphone or computer? How difficult could it be?

To receive money you just need a QR code (could be printed on a card like versocards.com).
Unfortunately for PAYING is not the same. You can't go around putting your wallet private keys on other people's QR code scanners.

Is there any solution I'm not aware of?