This is what I'm switching to. I would have suggested Textra, but when I downloaded it just now, TrackerControl told me there are a bunch of tracking libraries in it. Simple SMS Messenger, on the other hand, not only doesn't have any tracking libraries, but doesn't ask for internet access!

I've used other tools in the Simple suite and I love them.

Although I like using F-Droid, this app is also available on the regular Play Store as well.