Evaluate financing model? Possibly cheaper?

Yes, I do! Therefore, my question is not whether this is sensible. But I will be done after 25 years. My related endowment insurance with capital withdrawal would cover that, which I do not necessarily want. In addition, I can still influence the term through special repayments. Basically, I am asking for the best option to guarantee interest rate security. That also does not mean that I will remain single until retirement.