When you say your partner has been a saviour, is he the same partner as before?
You say that you are in a slightly better mental position now than before. I think you need to focus on being completely mentally well and confident. If you had children very young and they are all you know, perhaps you should take your improving life as a sign that you should do the things that you weren't able to do before. Education, training, a solid career. Imagine if 5 years from now you were a nurse, an office manager or a teacher.
You might not get your children back just now, and it might not be right for you to have another child, but if you are allowed contact with your children, and to provide them with some support, it would be a wonderful thing for them to see their mother recover and build a stable, independent and strong life for herself so that should the time come, you can provide for them.
You are still quite young, is that right? Maybe early 20's? You have another 20 years of fertility ahead of you. Push back having another baby for at least 5 or 6 years.
The desire to fill the gap in your life with another baby is very natural, and something that a lot of women in your position feel, but I think you should channel your focus into your mental wellness and building a stable future for yourself through education or training.