My first was very challenging, and I’m not very good at small children. He was the kind of baby where strangers would stop and comment “our second was like that, if it had been our first we wouldn’t have had another”. He was unhappy about everything till he was 4.
But then he bloomed into a much easier kid. And so we had a second. The second was so much easier! Slept better (still not through till he was 3), generally contented. Until he turned 4, when he discovered his voice and was unhappy about everything till he was about 7.
So the early years were hard, but we still had another. And now that they are towards the end of primary and secondary school they are generally delightful.
You don’t have babies forever (though those years felt neverending to me). They grow up, and change. Even if you had the easiest, happiest babies/toddlers it doesn’t follow that the rest of their childhood will be the same.
Prepare for the second to be as difficult as the first, and hopefully you’ll find it easier than you expect.
But equally, if you’re not feeling ready to have a second, then don’t. Maybe you’ll feel ready in a year or two, maybe you won’t. Make the best decisions you can for you and your family in the moment. If you end up with more children, then great. If not, then you’ll be able to give your all to the one.