Agree with others, it’s a very personal decision. There’s a 6.5 year gap between my sister and I (I am the younger one). Wasn’t planned that way but it took a while to conceive me as I understand it.
I’ve no idea whether it was stressful when we were young for my parents, I only got the impression that they were really happy to have us both and family life was very happy!
As adults we are very very close. The age gap matters not a jot when you’re grown up.
Also sorry to add this into the mix, not saying this should be a decider for you but when my mum was ill, then died, and then my dad died suddenly, having my sister was just incredible and I don’t think any other person would have “got it” in quite the same way. We had had the same upbringing and pretty much the same relationship with them and it made it so much easier to have someone to share all that with (not to mention the headache of dealing with probate, house clearing, dealing with the estate etc). Sorry to bring death into it.
Worth saying I know not everyone gets on well with their siblings.
Myself and DH only have one so far. We had always both said we’d want too but I think he is reluctant to go through the baby years again, and yes I do see how life with one is easier.
From my POV it’s not so much that I want another baby / to do the childhood bit again (I do) more prominent is the feeling that when my DD is an adult I’d like her to have a sibling.
In a way I can imagine us in 10 years still only having one, but in 20 years I can’t imagine it. Probably a weird way round to think of it!
Go with your gut OP I think. (Or let nature take its course....)