Oh my god, three years ago I was YOU. I didn't really want children, every time my partner brought it up I'd say "yes, but we have such a good life - we can have holidays, relax, sleep in... look at how stressed and tired X is all the time" and he'd just brush it off with the same dismissal. I was afraid of how much work it would be, and he seemed to think it would be a breeze, and everything would sort itself out.
The reason he thinks that, to be blunt, is because he's a man. Men have had a woman racing around in the background doing all the work children create, while they stand around with a beer gabbing about everything they know about parenting with the other dads, for generations. Usually in front of the football.
So I caved, thinking he kept bringing up children because he was generally keen on parenting and fastforward to now: I do ALL of the work. I still have my job, but ALL my annual leave is gobbled up by the days my son is off sick from nursery, has appointments, etc etc to infinity while he uses his days for rest and entertainment. My partner's answer to everything is "just get my mom to do it", i.e. where's the next available woman I can offload this onto? I am the one who doesn't get a shower every day, has stayed working from home, had to chip away at my own financial independence by reducing my hours, carry the entirety of the mental load involved in my son's health wellbeing and education. On and on for infinity.
You have the realistic, adult expectations of parenthood here, not him. And I would bet money that you would be the one carrying the vast majority of those responsibilities if you became parents because he doesn't even recognise their existence. You are right here.
BUT, despite this existential howling, and my current lack of sleep and hygiene, I DO love my son beyond words. When I look at him I actually feel IN LOVE with him. I have never found another human so physically beautiful, so charming, sweet and fascinating and worth every ounce of effort I can give him. So as much as I resent being a parent in the abstract, I do have a person who makes everything in life more important. and has probably led me kicking and screaming down a path of living a fuller life than the more self-centred one I led before.
It's really swings and roundabouts! Having a child is simultaneously the best and worst thing you will ever do in life. If you are the mom, it won't be just one of those things.