When I thought we were going to France in February I was concerned that funds could be held for days using unmanned fuel pumps so had a look on Money Saving Expert for pre pay cards. At that time the one that looked best for what I wanted was Revolut so I ordered one online.
It has an app and you can transfer money to the card just before you use it if you want to. You can do anything I can think you may want including setting an exchange rate where you want it to automatically buy or sell euros, (I thought they had clamped down on that years ago).
Look on the MSE site if you want a pre pay card and see what suits your intended usage best.