YANBU at all. And I agree with every word of the pros and the cons.
(could have written post myself also, am 44, dd is 6, only child, we are church mice poor although things slightly improved now I'm back working more regularly, have still got pram and other accoutrements despite being a confirmed parent-of-only-child- go figure)
I think the fact that you are seeing it as a maybe/what if/should I means you don't really want one. (transposing you onto me IYSWIM)
I think sometimes I want one. I want the teeny tiny newborny thing. I do not want the toddler bit when I'm nearly 50. I want to bf again. I don't want to potty train again yawn.
I worry about having a boy. I just don't know anything about them.
I definitely agree with JAMM that it mustn't be about other people. Dp (who is younger than me) has always presumed dd would be an only child because of my advanced years (harump) it's me who dithers. Dd would like a sister or brother, but realistically, until they're both in middle-aged years, a 6+ year age gap is never going to make them best friends anyway is it?
All pros and cons aside, do you actually want one? Yes or No? Because when I make myself answer that, with no justifications allowed, mine comes up as a No. If yours comes up as a Yes, then go for it.