I guess it depends on the decaffeination method but it might be worth some experimentation to find the right variety.

with any habit change, the less you have to think about it the easier it will be to make the change and to maintain it. Some hard limits can be good and have worked for me like no coffee after 12pm or limit the portion size to 1 espresso or 1 doppio but no more for each serving or only 2 servings per day, etc. I do think that at some level we are fundamentally lazy in the sense that it is easier to do nothing than it is to do something and it is easier to do something small than it is to do something big. That’s where smaller portions and adding steps to preparation (like storing the coffee less conveniently or do not grind more than you want at any moment even if you know you’ll immediately want more) can add friction to the coffee consumption process but also smaller changes are easier to adapt to and carryforward.