Hi. I have 2 girls who are 26 months apart. My oldest is 3 and the youngest will be 1 in a few weeks. I couldn't imagine not having my second child. It was a bit hard in the beginning to take care of 2, but after a while it seems like second nature. I know my older daughter loves having a baby sister and I know my baby loves her older sister.
But you are the one who will be pregnant, you should do what you are comfortable with. Your first child will be able to adapt to whatever you decide. It's good if you can give each child their own time every day. Since my baby takes 2 naps and my oldest takes 1, I am able to find time to give each alone time.