How do I go about it with an ETH address? Is that also sufficient? Can I just use MyEtherWallet and create a message similar to the one Theymos asks for when it comes to proving ownership for BTC addresses?
Unfortunately for OP (and ss far as I know) signing ETH address is not accepted method of proving the account ownership, and only signed BTC address is accepted, as mentioned by theymos in
Recovering hacked/lost accounts . If ETH address is accepted it would be mentioned there.
I remember a case of recovering a hacked account as recently as October 2020.
The stolen account was recovered using a signed ETH address. There is even a manual or description of the entire process that the owner of the stolen account created. It is written in Russian, but I think it will be useful as an example for the OP.
OP, I think you can do it. Good luck.
https://bitcointalk.org/index.php?topic=5284615.0