It is interesting to me that you have income and outflow so tightly coupled that you think in terms of "N% of income".
I did that for several decades. These days I take pains to decouple income and outflow. That is: I judge the expenditure on its own merits, whether I need or want it by itself, without regard to what % of income it might be.
Think of it like a leaky bucket: my paycheck goes in the top, and I control how much leaks out the bottom. Of course, I am lucky enough to have that luxury. Many people (most Americans) don't have enough income to decouple outflow from it, and are forced to think in percentages of income.
Sure - there's benefits to both ways of thinking about it. It's less that I tightly couple them and more that I find, for a sufficiently low percentage of my income, it's not worth stressing that much about the expense.
My mental model is quite close to yours for larger purchases ($100 or more, generally), but for something whose monthly cost is less than my hourly wage, thinking too long about if it's really worthwhile is probably not a great use of my time.
I did that for several decades. These days I take pains to decouple income and outflow. That is: I judge the expenditure on its own merits, whether I need or want it by itself, without regard to what % of income it might be.
Think of it like a leaky bucket: my paycheck goes in the top, and I control how much leaks out the bottom. Of course, I am lucky enough to have that luxury. Many people (most Americans) don't have enough income to decouple outflow from it, and are forced to think in percentages of income.