I know my financial position. For me when I was single, energy spent on personal finance was energy lost for other causes, like earning a lot more money for example, or doing something socially relevant or building a laser cutter.

But my signifciant other? Living hand to mouth on a tight income, and not mentally prepared to even think about budgeting.

So now as a couple, needing to nudge her into basic budgeting, it better be with as little friction as possible...

Something low tech that really helps with that by the way is day-by-day budgeting. Estimate your annual net income minus your fixed costs: mortgage, rent, utilities, insurance, savings, investment, ... Divide this disposable income by day/week/month/quarter/semester/year. You now have one number per timeframe not to exceed. Discuss everything exceeding this limit, and build sensible rules from that.