Monzo have monthly cash withdrawal limits I believe, or if not they start charging a fee on each withdrawal after some fairly low amount. Premium bonds are an option; of course you can cash them in but not on a whim in 5 minutes.
But the truth is, it doesn’t matter where or in what form you put your money, if you want to find a way to gamble with it you will. My best advice would be accept you’ve had a good streak, sign up to Gamstop for 6 months, bar yourself from land based bookies and casinos and enjoy the money.