I say this with deep respect for you.
Having a child is NOT the right response to being broody. Being broody is a something you are experiencing now. Parenting is for life. You became a parent at 16? It is all you have ever known. There is more to life and relationships. Other things to look forward to - education, jobs, promotions, travel, etc. all of these become infinitely harder the more children you have before you have.
You have two children. I’m sure they are beautiful and lovely and deserve a Mum who is well, happy and able to meet their needs. Not only now but in the future. What if baby three tipped your mental health in the wrong direction? What if in year 6 one of your children started to struggle, would you have the skills and means to either sit with them every night for an hour or more to help, or get a tutor? Or would you already be too stretched? Kids needs don’t diminish as they get older, they increase in ways that require more creative and flexible parenting. It isn’t as simple as getting up and feeding them or changing a nappy. You don’t need to be wealthy to be a good parent, but you do need to exercise wisdom. It isn’t about what you want. It is about what your children need and deserve.
if you and this boyfriend are still together and are thriving when you are 30. If you can meet the needs of your children and they are thriving at older age. If you are mentally well, if you have the finances, then maybe it’s time, then. Between now and then find other things to look forward to - mental health stability, a job, or course, volunteering at their school. Something that isn’t just more dc.
Being a parent isn’t actually about having children. It is about a 20+ year commitment, planting the seeds that help them grow and flourish long term. That includes time to support their education, give them experiences, be there to help them navigate hard things which only increase with age and if I’m honest break any cycles that exists in families - whether that’s a cycle of poverty, broken relationships, teenage parenthood. Our kids deserve us to be willing to do this. To show them with our own actions, not just words. It is hard work. It is taking the spotlight off the ‘big’ things that bring us excitement and doing the daily grind that lays a solid family foundation. If your daughter was you, would you want your life for her and another baby? Or would you hope there were other opportunities she could have too?
In your situation I’d focus very much on laying that foundation. Your children already have major losses. Look at what a commitment to them and them alone right now could give them. It’s priceless.