Having another baby but not with the my original baby dad

When I was pregnant the dad was never excited. He hardly took notice of me and I was upset all the time. I thought it might bring us closer once I told him but from the day I told him to the day I gave birth he didn’t really care. The first few weeks of my son being born he wasn’t too bad, he would cry and feed him and change him with me saying but he would never do anything himself. We broke up and both moved on and I was wondering was would be a good time to have another baby? The guy I’m with now is amazing. He’s taken on his son like his own and looks after us both very well. He does get upset that my son ain’t his and would kill for him to be his own.

So when would be the right time?