First - please don't have unprotected sex with a "if it happens, it happens" attitude. Becoming pregnant - or not - is not a sign of any kind. Talk with your husband honestly and then decide. This is too important of a decision for you, your husband, your marriage, and your kids to leave to chance.
That said, it is totally normal to look at babies and feel nostalgia for the baby days. I'm the woman who plays peek-abo with toddlers across the restaurant when their parents aren't looking. I love holding friends' and relatives' babies - rocking them, feeding them, I'll even change a diaper to give the parents a break. When I leave them, I miss the baby stage. And then I go home, get a shower in peace, sleep through the night and realize how good life is now that we are out of the baby stage. My point is that it's completely normal to look at a happy stage in your past and miss it. But there is no going back in time, and you can't recreate the past.
You should have another child if both you and your husband are ready to embrace all of what a new baby could be - boy, girl, typical, special needs, colic - because you don't get to choose what kind of baby you get (I know you know this, but from your post it sounds like you are imagining a theoretical perfect baby, not reality, and you need to accept reality of all the possible things a new baby might be before you make a decision).
ETA: Well, I have 2 siblings who are 6 and 5 years older than I am. I also have a younger sibling. We joke that we were 2 different families. I was not close to my older 2 siblings growing up. We just didn't have anything in common. And I know that oldest sibling resented having to babysit and I resented my bossy older sibling telling me what to do. It was also quite different because I had the younger sibling to play with, so when my older siblings paired off, I could pair off with that sibling to play our own age-appropriate stuff. At amusement parks, one parent would spend the day in the big-kid part of the park with 2 kids while the other spent the day in the little-kid part of the park with 2 kids. It worked for my family, but it was a small town in a different era - my siblings could walk to their sports practices and dance/music lessons. I wasn't forced to spend all day riding in a car while my mom taxi'd older kids to their activities, etc.
I'm not saying that it can't work. Plenty of people have 3+ kids in their families and love every minute of it. I'm saying that you should go into this with your eyes open about how it will change your day to day life.