Hmm. I downloaded Signal and saw that no trackers were detected, which is good. But it appears it doesn't do SMS anymore. I couldn't text anyone who didn't have Signal. So that's s no-go for me.
Yep, the hardest part of Signal is convincing everyone you text to use it. Though, once you do, it's awesome!
SMS as a protocol is pretty bunk. I'm not sure any app can save it. That's why I just stick to the default SMS app. Well, that, and because that app is made by Anrdoid and your carrier, who can already track everything anyway, so there's no (extra) privacy hit.