Firstly, menses and ovulation are not related. So, even if you have menses, you may not be ovulating. Likewise, even tho you have no menses, you may be still ovulating. So, you could be fertile anytime regardless whether you have menses or not. I learnt it during my fertility treatment when I had prob conceiving.
I asked my gynae the same question when I was bf my first child and wanted to try for second one when my first son was 1 yr old. As Ihave prob conceiving, gynae advised me to stop bf when I want to try for second baby. This is bcos during bf, our womb will contract and it is not ideal if we are preg. But then, if you have been healthy, it is ok. I know of mummies who bf their first child till after first trimester. In the end, the child is the one who doesn;t want to be bf as once you are preg, it is thought that the breast milk will turn sourish and not appetising to the kid anymore.
What I suggest is perhaps introduce fm first to your child and do partial bf. Just in case you are preg and suddenly baby doesn;t want your milk, at least baby still can take fm. I had prob weaning off my son. took me almost 2 weeks before he accepted fm. What i did was to mix 10ml of fm to 170ml of ebm and slowly increase fm.