Doesn't anyone ask what rent would cost you with a child in comparison?
Counter question: How is one supposed to calculate that?
No one knows how old he will get and how long he would still have to pay rent in life or how rents will develop in the next 20-30 years, during which financing could also be running.
If the incidental acquisition costs are covered, there is still some reserve for a safety buffer, kitchen, furniture, garden, etc., and she could actually be happy with a terraced mid-terrace house with a small plot of land, then I would advise the OP to buy.
Sure, financing would look nicer with a significantly double-digit percentage of equity – but until that is saved up, prices have galloped elsewhere. What costs 300,000 now will cost 350,000 in 5 years at the current rate – and then the equity saved until then will not be enough again.
Waiting currently gains nothing. This is written by someone who himself was long under this mistaken assumption.