Deciding to have a baby

Some women "just know" they want to have a child - which is fine and good. My question is for those women who are or were on the fence about having them. What made you decide that yes this is something you definitely want to do?

I'm 35 next month, and I had assumed that I would have them one day, but have actively avoided pregnancy until now. I'm obviously staring down the gun of reducing fertility with age and the "babycrazies" still haven't started. I'm in a stable loving relationship and made it clear even starting the relationship that I wanted kids so we would be on the same page about something so important - but that was 2 years ago when it still seemed a long way off. Now it still freaks me out - a lot - knowing that theoretically time is starting to become an issue (yes older women conceive - but we know it can be harder etc) so really, the time to start is now. However the financial, emotional and physical changes that come with having a baby (that won't even be a baby that long!) still seem so huge - there are so many things to consider and my body or brain or heart still don't seem to be able to say yes with conviction. I don't want to have a child based on the fear of running out of time or based on an assumption that I "just would" that I had in my 20s. I enjoy my friends children and my nephews and nieces are lovely but somedays I'm also happy to be able to walk away from them at the end of a visit.

What made you actively decide to have kids - or not, if that is the case?