I was not asked to reply, not being an only or having an only, but I just can't resist throwing my thoughts into this thread. Everyone has there own magic number and whatever you have will be perfect for you. All will turn out fine whether you have more than one or stop at one because THAT is your family. Only you & your DH can make this decision. But I thought I'd share some of the thoughts on why we had more. I hope it just doesn't come out all over the place.
I'm number 3 of 4. I'm fairly close to my oldest sister & my brother. None of us really like my second sister much. She's someone I wouldn't have much to do with if she wasn't my sister. But she is my sister. And I'd be there for her, for anything if she needed it. We're not friends, but we do have a bond.
No one else knows your family history, but siblings because they are the only people who are part of your family. I mean immediate family here, not extended families with cousins. They truly KNOW everything about where you come from and what shaped your personality--even if they are different. Only a sibling can understand inside jokes. With an only, there are none.
Yes, siblings fight. Even as adults. But as a parent, even though it drives me nuts sometimes, I wouldn't change that. You have to find common ground as a child with a sibling, not so much with a friend. Friendship ends. DNA doesn't. It's a wonderful skill & learning experience. I hate listening to my kids fight and I know as they get older it will get worse. But I'll take that any day over a quiet house. I think you can learn sharing better at an earlier age too. My kids are closer in age than my sisters' kids are, and mine share better. Even the one with the difficult personality.
I had a friend who referred to our child as only children (before we had our second) and I just couldn't figure out what she was talking about. I never thought of DS#1 as an only child, simply our first. Basically, I knew our family wasn't complete. It still isn't, we're about to start trying for #4. There is just an empty spot in my heart. Love only grows with more. Love is not finite, it's infinite. There is more people to love and more people to love you.
I also want my children to have each other as they grow older, even if it isn't the talk on the phone daily/weekly type of closeness. They have lots cousins, but so did I and it just isn't the same. They will be there for each other if our health declines, when we die. If not doing the physical work, sharing the pain and other mental burdens. And they will have someone after we are gone. Their roots will never be dug up, but remain in firm ground.
Life is precious. It can be taken away at any time. A good friend of mine had a brother until college. One drunk driver later and he is an only child. He wasn't close to his brother growing up, polar opposites. But as an adult with children of his own, he misses him terribly. So do his parents. Now that would never change regardless of one child or a dozen, but at least there still is that connection later in life. Of course, I wouldn't have a child FOR another child, that's kind of like getting a pet for a pet...
We've always fit each of our 3 kids into our lives v. changing our habits just for them. While I've always needed to make adjustments with the addition of each family matter, it hasn't been a total upheavel. I certainly never had to be home at 12:30 so my child can take a nap in his crib. He can sleep later (#3 has the adjustable naptime) or he can nap in his stroller/carseat/where ever (the case of #1 & #2). It works for us. So that never stopped us. If I did it that way, I'd be a virtual shut-in and we'd all be miserable. So "all that extra work" just didn't exist in our case. All 3 of mine have strep right now. Not fun--DS2 on WEd, DS1 (today) on Thur, and DS5 today (Friday). But, I still wouldn't change it for anything in the world.
People talk about the cost. And, yes, every child cost more. But each costs less than the one previously--especially if the same gender. You don't need to rebuy cribs, bassinets, swings, bouncers, etc. Toys and clothes are passed down--I don't think DS#3 has but two new outfits ever & he's one!! Nor has he ever gotten a new toy except one at Christmas last year (baby toys are the same regardless of gender). When he had our third we received mainly money/savings bonds/stocks to go to his college education for gifts. And while we pinch pennies, each child has one year of college education completely paid for. It only takes a little at a time while they are little.
OK, that isn't all of it, but that's enough to mention. Again, remember, what is right & works for someone else, might not for you. It's a personal decision. And it will be the right thing in the end. If you think, however, you might have regrets--you're not done. The biggest reason to have another is that it just feels like someone is missing.