Thank you for your quick responses. In our area in BW, the rental prices for comparable houses are rather >2,000€ cold/month. With an alternative financing option, we could reduce the monthly burden from 3,200€ to 2,940€ and would pay it off a few years longer. That would probably be the safer option...
I always say, as long as the loan interest is lower than a NKM and the loan rate fits within the budget, there is no objection. Although 43% of the household net income would be too high for me. On the other hand, with 5-8% inflation per year, the ratio will probably turn in your favor in the foreseeable future and you have fully financed anyway... so the rate remains the same until full repayment.