Oh Bless you, OP.
I only have one child {He was a delightful, easy baby..and is now grown up} But had several health visitors and older nurses at the baby clinic say ''He's so good and sweet natured, you won't be as lucky a second time''...{I thought ALL babies were easy like him..} 😆
They said ''Think very hard before having another, as often mothers of 'Easy' first babies get a shock having a second..as they all come out so differently!
I did heed their words. I couldn't imagine loving another child as much, and didn't need another.
When DH left {when son was 4} I was very glad I only had the one to care for.
I DO get absolutely what you mean by ''wanting to do things correctly''- With son, I made many mistakes- I would have been far more tolerant and patient with another , The first child is the one we ''learn on''.. First kids are the trailblazers for any kids that come after.
Don't worry, time flies, before you know it, both will be grown and independent.