You may desperately want a child, but agreeing with other posters, it's not at all necessary for your child to have a sibling, and they won't be missing out from it. I'm an only, I've always been very happy with it, and while I do have cousins, we're not at all close. I also have many friends who have one or more siblings, and I would say that close sibling relationships seem to be the exception far more than the rule. Most seem to see them just a couple of times a year, and some actively don't get on with them. And it's very common for just one sibling to be left with elder care, while the others don't contribute. So don't project all those hypothetical reasons onto your child, please own that it's purely your own desire, and that's fine.
Good for you that your experience as an only child was positive, but that's not the case for everyone and certainly wasn't for me.
I was an only child.I had a lovely childhood in many ways but there was always somebody missing.I would see friends with siblings and desperately wish I had that too....when friends went home i felt empty.I had a big home, big garden, all my parents attention, plenty of money, privelidge and opportunity, and they gave me pets too.
But it didn't make up for being on my own.I used to wish on my birthday cake and when throwing stones in the sea or stirring the Xmas pudding, for a little brother or sister.
As an adult, my father died afew years ago, and all my mum has is me.....I live close and so will be here for her, but if I was someone who wanted to move away, live abroad or something I couldn't have done that without leaving her alone.
When I watch my two children play together, I feel so grateful they have each other....and realise even more what I missed out on.
Yes not all siblings are close, but when the parents foster their relationships and handle conflict well, many are, and they can really enhance childhood and beyond