At minimum, I spreadsheet my big decisions. I put in all my known factors: budget, TCO, alternatives, a weighted list of pros and cons (weights according to factors important to me or ability to solve the problem at hand), etc.

For really big decisions, I build a decision tree with dynamic branches. For example, when buying my most recent house, i had inputs for interest rate, points, house inspector rating, cost to move my sailboat to my house, average luminous flux received, etc. Data in these fields adjust other fields like TCO and budget, which then shift the decision tree one way or another.

It's excessive, but I do it this way to help me avoid missing some big variable.