Child spacing

My partner and I want a second child, we already have a 9-month-old baby, and I keep thinking what is the best thing to do for both of them, my baby and the newborn. How long should I wait for?

I think about how jealous she could get and if it'd be much easier to handle her jealousy as a baby. And we don't want to wait too long either (I've experienced having a sister 10 years younger than me and I am more kind of her mum rather than a real sister).

What's your opinion? Sorry if I've made some mistakes, my mother tongue isn't English.