PeterB, one of the mistakes LBSs often make is introducing another person into their situation. These situations are complicated enough, but when the LBS goes against wisdom and starts dating too soon, it just further complicates things. There are a lot of reasons for this, but trust me, it rarely ever makes things better.
In your case you are being tempted in your own mind, it seems, to be wanting another child. So that would be introducing 2 more people into your situation: a new mother (since you have already said it is impossible with your STBX) and the child. You will have plenty of time for that kind of thing later. Right now concentrate on moving your life forward, being the best dad you can be, and setting yourself up for future relationship success. There are no quick fixes, no bandaids to these things. It takes time and work to reach the next chapter of your life.
Agreed. The thought came up when I asked myself why I should or should not stay married to her and what could be good after D if we ended in one.