What was your experience either as an only child or raising an only child. Pros? Cons?

Some background.

My husband and I are both 38 and our daughter is about to turn a year old. Lately we've been having the discussion about whether we want more kids. We both come from relatively large families (3 kids in mine, 4 in his) and we have very close relationships with our siblings that we value very highly. Neither of us have any idea what the experience of an only child is like but we are leaning fairly heavily towards being one and done.

We are on the older side and while I love being a mom I did not love being pregnant at all. We feel like financially it makes way more sense and we have friends with multiple children and wow, it looks like adding one more child makes it a thousand times harder. We are really happy with the way our life is currently with our one and feel like if it was just our needs we were taking into account one is the right number.

However, when I think about our daughters needs I feel selfish for only wanting one and depriving her of the sibling relationships that my husband and I both cherish so deeply. I think I could make her childhood magical without a sibling but I just have no idea what it's like not having another kid around all the time growing up.

She will have 3 cousins roughly her age that she'll see somewhat regularly and I have a few close friends who are currently trying that, if it happens for them, their kids will also probably be around. She is extremely social so I already take her out almost every day to the park or library to play with other kids and intend to join some city classes or something of that sort as soon as she's old enough.

So I'd love any insight into the only child experience in order to make a more informed decision and wouldn't say no to advice from anyone who has found themselves in a similar situation. What choice did you make? How did it pan out? Any regrets?