Your bank card underneath a protective phone case will do the trick my friend, noone will ever know the difference. I go old school myself and just keep my card in a wallet.

On a serious note, i just used my banks own nfc app, which got a bit glitchy so i stopped using it after i couldnt pay to get on a bus with it. They are discontinuing the service now anyway so c’est la vie i guess. Its not foss, but if your bank has an app that has the feature, then why not, they know everywhere where youre spending your money anyway right?