The school must have a policy on data protection and that often includes what standard information is held about a child. It would include Sats results, data on progress, pastoral care, attendance, ethnic group, medical, SEND. Plus other confidential issues which might have arisen.
If the school has stored emails specifically about your child, then they should be held securely and are part of the data held by the school.
However, if a new school has a place, they cannot refuse to give it to your DC based on a report from another school. If you are the only parent wanting the place, you get it unless SEND cannot be met and discussions have to be held about provision. Even then they cannot ultimately refuse if they are not full. Your existing school is highly unlikely to be difficult about your DC moving. Why would they be?
Regarding the governors: they are not allowed to have private chats with parents about DC or policies at the school and how the school is run by the Head. You must go via the complaints procedure so what you were told is correct. As a current parent you could do this. However you won’t gain anything if you are leaving but you might feel better! Give them a blast about not following their anti bullying and behaviour policy! And victim blaming. Ofsted is not worth it.
We transferred a DD out of a school and it was worth it. Just go and forget about this school. Try and keep in touch with his friends but he will soon make new ones and old friends might drop away over time. Good luck.