Anon, I have just a slightly different take on all this.
I, too, was a strong, happy career woman in a marriage with my best friend. He and I talked about kids and how they would change us, and we were unsure for a long time. I, too, searched for something that would make me "know" it was right. I just wasn't born with the "I always wanted kids" gene. I was born with the "Someday, maybe" gene.
Here's what I'll tell you. If a person who had no dogs asked you why you had them, you'd barely know where to start. (I have three.) Explaining the intangibles about having a dog is easy, but I think understanding them is hard. That person without a dog might say, "but they bark, they shed on your clothes or your furniture, they're expensive, they get sick, they pee in the house sometimes," and on and on. You could try to explain how none of that makes a bit of difference -- and, in fact, how all of that is actually beside the point, you know? But somehow, the person without a dog still doesn't understand until they love one of their own. I just don't know how you can actually communicate such a thing so that another person almost experiences what you're saying.
I think it's the same about kids. We can try to pull it apart, to ask the questions, to listen to the answers, and to have intuition about ourselves -- but I have the feeling we never get the whole story unless we go ahead and take the leap. The unexplainables are just too big. But I think that in the end, the noise, the mess, the difficulty -- they all end up being side issues, just like the barking or the dog hair.
I will counsel you this way, though: If you think you want to try, don't wait too long. Don't spend all your time going back and forth and looking for the answer that helps you know for sure -- it just may not come. And those last years of fertility are special. If you think you want this, you need to go for it before it's too late.
We waited. We waited too long. We tried, and then we found out we had some small medical issues on both sides. We addressed those, tried some more, no luck. We made the decision to explore adoption, but it gets complicated when couples are "older" (I can imagine your distress at thinking that you are an "older" couple, and I shared that distress!! But it's a fact in the adoption world).
We ended up without children. We're very happy, even though I wish we'd been able to have some. We dote on our 15 nieces and nephews and spoil them with our time and love endlessly. So you'll be happy either way. But there IS a deadline for biological kids, and if you decide it's important to try for them -- to bring a smart, cute, artsy kid into your world -- don't wait too long.