- Edited
I can only add to the good answers given by the previous speakers:
Consider the eternal security vulnerabilities of iMessage.
Most zero-day exploits were in connection with iMessage.
That's why I have deactivated iMessage on my iPhones for years and only use the iMessage client for receiving SMS (some companies still send SMS, sometimes still 2FA, otherwise I wouldn't need SMS at all).
The email client was also very dangerous with iOS, which is why I had even deleted the email client.
With Tutanota, I have a secure email client with E2EE.
As a messenger, I am using Threema since December 2020 and additional Session since September 2022.
If I were you, I would tell all my SMS contacts about the planned change and suggest Session for confidential messages, because hardly anyone wants to pay money for a messenger and some people would have to use a (different) messenger just for you.
I don't think Signal is safe because it requires a phone number and unnecessarily supports MobileCoins.
But if you trust Signal, then it's similar like me with Threema and Session:
With Threema I have the most contacts and conversations with friends. Session is my plan B, if Client-side scanning or Chat control is coming (https://www.patrick-breyer.de/en/posts/chat-control/) andThreema could not defend itself.
I've been a happy user of a Pixel 7 Pro with GrapheneOS since March. :-)