Basically that's it: How to properly present an ultimatum?

My story in short, I [32] want children and she [31] keeps delaying it.

Always says that we're gonna get onto in in 2-3 months, but when time comes, she finds some reason to delay it. It went on for 2 years now, and I've had enough of it at this point.

We are having a lots of fun BTW, sex is awesome, she isn't using me as a provider, etc, so besides this "elephant in the room", we are getting on great. We do not use protection, but pulling it out is way too effective.

What I tried, and obviously failed:

  • using logic (reasoning and shit, yeah, dumb move)
  • telling her I won't pull out
  • telling her in an assertive way: I want children and what she does is not the way I like the things going and I want her to change it ASAP as I do not want to waste more time with "give me some time"

None worked. But that's the past. The present:

I'm on the edge of getting the fuck out. But I want to give ourselves a last chance. I want to present an ultimatum, either we are getting on it NOW or she should move out.

But how to present it in a way that she doesn't feel attacked, cornered, etc. because I think people's response in this situation is pretty bad (negative, defensive, way more emotional than should be, butthurt, offended)? I also want to avoid her saying "okay do it", but then having this "you forced me into it" mindset.

Any suggestions are welcome, thank you guys!