Excel table. Once the monthly fixed costs, the annual fixed costs broken down to the month, and then the variable costs. Simply always get the receipts, set up a box in the kitchen, and always put them in there. At the end of the month, invest an hour and enter everything.
On the topic: I stick with the tight budget. I also strongly recommend, like the previous speakers, to analyze the last year based on bank statements. That opened my eyes two years ago. One of the first actions was to open a comparison portal and compare all contracts. That was VERY worthwhile.
And I also continue to warn against overextending yourself. Based on the interest rate of over 1.2% for 10 years, you can see how the bank assesses it.
My urgent appeal to give you certainty: sit down tonight and write down ALL costs from the last year. Trash, phone, mobile, simply everything. Special expenses like hairdresser, nails, etc. Consider clothing, cosmetics, and so on. As precisely as possible. If you then have the monthly rate, plus additional costs, plus maintenance reserve, minus current warm rent left over, THEN it might be possible. And only if the cars are still included. The costs also TÜV, tires, wear and tear. Oil changes cost between €70 and €250 for example and significantly contribute to durability. If the washing machine breaks down, the €400 should not hurt.
If you drive an old clunker on TK and have a self-inflicted accident in winter, the €3000-5000 for the next car should not hurt. And so on and so forth. Only calculate with legally or contractually agreed subsidies.
The inheritance must be urgently disregarded. No one knows what will happen.
The heating for example CAN still run for 20 years. Or the CO2 taxes force replacement, or something else breaks. Or the tanks are getting old and need to be replaced.
Or, as happened with a well-known manufacturer, an important small component was no longer available and the heating could not be operated without it.
If it breaks down in 5 years along with the car and the washing machine, the €13,000 must be there. Not maybe, not possibly, but they must.
The house is certainly undervalued and I would take it too. It really looks pretty. But even a pretty, undervalued house costs money and you have to be able to afford it.