That's really great! We also planned conservatively and included a bunch of buffer, but knowing myself, I don't want to give up anything and always want more.... then there won't be any buffer left either
With that attitude, you might soon have to fall back on your securities...
And no, I don't know your financial situation, which (no offense) I don't care about, because it's your business. You have to feel comfortable with it. I just said that it wouldn't be for me.
As for the bank: I have heard of cases where customers were offered 1% repayment and loans they couldn’t actually afford. That’s why possible securities are no guarantee for sustainable financing. In the beginning, everything usually seems great... the harsh awakening comes only after the regular term when you realize that you can no longer afford the house because either interest rates are higher now or the calculated repayment didn’t work out.
We also faced the choice of a 30-year fixed interest period or 20 years at significantly better conditions. It now costs us €300 more in repayment per month, but hey, I want to be done someday. I don't live just for the house and enslave myself for it. I always say: the house must serve me, not me the house!
And as you write that you don’t want to give up anything: do you seriously think you'll carry thousands of euros every year for 25 years to the bank for special repayments, or wouldn’t you rather spend the money on things you want to afford? I bet on the latter... and suddenly... the concept goes out the window.
I find banks that allow this irresponsible, sorry. Because if the financial background were so excellent, you wouldn’t have to take on so much external capital. And only in that case would I not worry.