Kate, I am just now seeing this thread. I am so sorry the cute little thing did not make it. My mom and I had a bottle baby when I was about 10 years old. I had it in a shoebox by my bed and woke up in the middle of the night because I heard it trying to breathe. I got my mom and we both sat there and cried while it passed. I remember that time vividly, so I know exactly what you are going through.
RIP little baby.