Agree with the conclusion, disagree about which line does the damage.
You have heating as the surprise. For me it was the exchange rate and the cost of holding money in one currency while earning in another. Over a year that quietly took more than a bad winter ever did, and unlike heating there is no month where it stops.
The second thing nobody budgets: the tax position. Depending on where you are actually resident, staying somewhere long enough to be comfortable is exactly what makes you liable there. So the advice "stay put, it is cheaper" is right on the spending side and can be expensive on a completely different line: the two pull against each other and no budget spreadsheet I have seen includes both.
Not saying do not do it. Saying the version of the plan where you sit still for eleven months has a bill attached that the moving version does not.