From a different perspective.....
Firstly I completely agree that your smp should be relevant to how much you earn.
Secondly, I thought we wouldn't be able to cope, and tbh we struggled for two years because once ds1 was here we didn't want to put him in child care and we have no family to help.
When you have a child, you will obviously have the basics still to pay like mortgage, utilities, council tax etc. but I can honestly say hand on heart I would choose to struggle financially than send my baby in to child care
But that is my personal choice. Since ds1 turned 3 he's been in nurseries etc and lives it. But for me, they are babies for such a short space of time, I wanted to spend every minute with him.
Also, look in to getting a mortgage break. We did with both our ds's for 6-9 months each time(I can't remember exactly) Obviously they still add on interest, but we didn't have to pay the mortgage for nine months which was a huge relief.
My advice would be to see how you get on. Your priorities change and life changes so you may find yourself ins different position once it's time to go back to work. And worry as little as you can. You will manage
Good luck with baby 