Hi summersun - welcome to Askaboutmoney.
I think an interest-only mortgage is a good idea. A repayment mortgage means that you are paying the interest and also, in effect, saving. It makes no sense for the two of you to be trying to save just when you are going through a very expensive time in your life.
The downside is that in 20 years time you will still owe the full amount of the mortgage or €137k. But that will happen only if you make no capital payments. Try to get an interest-only mortgage but when your finances are back in order, start making some repayments of capital.
Brendan