Interest rate security is important to me too, but you have also secured the large amount over 25 years with option A.. So after 10 years you only have an interest rate risk of €28,000. Even if you repay less here and it is €40,000... This amount is absolutely manageable. And before you put €80 into a [BS], better use it to repay, then the residual risk becomes even smaller. A bank always earns with a [BS].. just the closing fees alone are huge... that also results in a nice repayment :-) Above all, you tie yourself to one bank, who knows what it will look like in 10 years.. interest rates maybe at the same level, a bit lower... then you can special terminate the large loan and be flexible in choosing a bank.
Is option B cheaper?? Hmm.. take a close look at what you pay here. There is always a repayment overview with a detailed breakdown of the interest. THAT does not lie and I would only believe that (unless your brother/father works at the bank and definitely does not want to earn from you).
I don’t want to badmouth banks here, not all are the same but they all want to make money off us :-) That’s their business after all :D