You don't want to go back to a key meter, that's always more expensive and also means you can't (as far as I know) smooth costs throughout the year, because you have to pay in advance so costs a lot more to use heating during winter.
If you don't switch supplier or take a new deal, you will go onto the price cap tariff, which, while being a lot more expensive than what you're currently paying, is generally less than available fixes.
Some suppliers are offering 'loyalty fixes' which are not as expensive, but seem to be slightly more than the April 2022 price cap, but give certainty for next winter, and are likely to work out cheaper over the next year, if the price cap goes up again in October. But if prices fall, you could be locked into a higher price next winter, or may be able to switch, as these often don't have penalties if you leave early.
But whatever you do, compare unit prices and standing charges, not any quoted monthly direct debit prices, because some suppliers, and Scottish Power have definitely guilty of this, have been quoting monthly prices for long term fixes based on a lower amount than what you use, and they'll let you run along with it for a few months before going, 'oops, looks like your usage is higher than the unrealistically low estimate we buried in the small print of that contract you signed without reading properly, looks like we'll have to increase your direct debit'.