Is purchasing a house and complete renovation affordable?

That is very optimistic thinking in both cases. Your children will then have children and absolutely no time to maintain grandpa's huge garden. Especially since they probably won't even live around the corner but possibly hundreds of kilometers away.

And selling... the house you have lived in for 30, 35 years? Where you designed the garden yourself, built the terrace, celebrated parties, raised children. You are among the few who can just let that go and move into an anonymous apartment in the city. Usually that does not happen either. The garden is more likely left to fend for itself or a gardener is hired for a lot of money every few weeks...

Believe me... once you have lived there for a few years and a lot of sweat and especially money has gone into it... you no longer see it soberly as a stone box that you neglect and move on.

You notice it yourself, right? Today you are willing to put your over-65 self through moves that you yourself, young and flexible today, would rule out.

Instead of living in dreams where you already see your grandchildren living next door, you should be brutally honest about what a payment of that size means when only one income is coming in. Taking responsibility for future children doesn't mean securing a garden for a trampoline, but that you don't become a slave to the loan to which you subordinate everything.

That's unfortunately all quite nonsense. Dieter Nuhr once said it nicely... "The extra years you gain through healthy eating, sports, etc... you don't get them now... you get them at the end, when you are old, frail, and demented..."