There needs to be middle ground here.
You’re absolutely not wrong to not want to remain friends after you split, but you have a child together. Thinking that it’s ok to do all your communicating through a twelve year old is not the answer either and puts a lot of responsibility on your DD for the way your relationship with her mum has turned out.
Given you have a child together it is inevitable that you will need some communication between you, and for the sake of your daughter it is preferable that this communication is amicable, even if you can’t bring yourself to be friends.
What are the current arrangements re contact for instance? How far apart are you going to live and who is going to be responsible for your DD getting between houses? Also, things like maintenance need to be taken into account for your DD, how are you planning to work that out?
My DC are mid teens now and the vast majority of contact happens between them and their dad. But at twelve we reached points of them e.g. not wanting to go to his, not wanting to go on family holidays with them, not having a decent relationship with his partner etc and it would have been entirely unreasonable to expect that they be able to navigate that on their own as twelve year olds.
Like it or not, the fact you have a child together means that this isn’t a relationship you can just walk away from without a backward glance.