I''m sorry for your loss and and I'm so sorry you are going through this.
I went through something similar with my first. I also didn't make enough milk with my second either. I combi fed both successfully (first until I stopped at 2.5 years and 2nd is 9 months).
-You are doing AMAZINGLY! You have been through so much and you are still giving your baby breastmilk. That's an amazing achievement.
-You are breastfeeding!! Combi feeding is breeastfeeding! And you are doing what's right for your child by giving formula too. Formula is amazing! It's what's allowing our babies to be super duper full and grow and develop, alongside breastmilk.
-SO MANY PEOPLE use formula. I live in like the most hipster yummy mummy breastfeeding central area of London and I see people using formula ALL THE TIME. Lots of celebs too and lots of people you wouldn't think.
-It seems like it's really important how your baby is fed now. That's natural; that's biological, it seems all consuming and all you can think about. But I promise promise promise you, in a few months it will matter less. And in a few years you won't ever think about it at all.
-If you want to stop, you can stop! You have tried and done amazingly well.
-If you want to continue to breastfeed, my top advice is put baby on boob as much as possible. They learn to be more efficient and start draining your boobs more and more the more they are able to feed. I fed mine every 1-2 hours. BUT if you can't be fucked to do that (totally understandable) you can just be consistent in feeding baby x times a day and there should still be milk there at those times.
-If you want more general support; there are professionals (IBCLCs) that can come to your house or do online chats to help you meet your goals, whatever they are. The right ones do NOT judge formula feeding or bottle feeding.
YOU ARE AN AMAZING MUM!!! ❤️