You essentially need someone with the structural incentive to limit excessive spending to be in a position to actually do that. In the original design that was the US Senate, because Senators were elected by the state legislatures who would then prefer programs to be implemented at the state level unless there was a reason to do them at the federal level. It's not a coincidence that the massive expansion of the federal government happened pretty much immediately after that was changed to make Senators directly elected.

Changing it back would probably work, but it's also a good example of the kind of thing that can work. You find someone whose incentive is to say no unless then answer should definitely actually be yes and you give them the ability to say no.