What can I do to make this easier for my daughter?

My daughters father is a narcissist and we do not live together. We pretty much have 50/50 custody. Over the years I have struggled with him thinking he knows more then doctors or anyone for that matter. My daughter is 8 years old and has started going through puberty. I have bought her training bras and she has not worn them consistently.

This morning while my daughter was getting ready for school she told me that she wanted to wear a training bra. She told me that yesterday she looked in the mirror at school at felt like her breast were sticking out and it made her uncomfortable. I asked her if she wanted to wear them from now on and she said she did. I asked her if she wanted me to talk to her dad about it or just buy some training bras for her to have at his house. She asked me to just talk to her dad about it and where the training bras are located in the store so she can find them.

Now when I first bought her training bras her father said she was too young for them, which I told him that I was the same age as our daughter when I got my first training bra. So when I told my ex about the conversation I had with our daughter this morning he said she is too young to be going through puberty. Which I sent him screen shots from the Mayo Clinic describing exactly what changes our daughter is going through. He can’t take my word for it. He needs expert documentation.

Also, I told him that he is not going to make our daughter feel more uncomfortable about her changing body. When we can do something as simple as let her wear a training bra to make her feel secure with her body.

Has anyone else dealt with a similar situation? It’s always a constant battle with anything medical with our daughter. Or any change. We have also had issues with him shaming her for bed wetting even though I wet the bed when I was her age and eventually grew out of it. When I spoke to a doctor regarding this she confirmed that bed wetting his hereditary. I tried to explain to him that she can not control it, but he thinks she can, which the doctor confirmed.