I am assuming google messages handles SMS?
I use Cheogram. It's FOSS, runs on jmp.chat's XMPP protocol, and can bridge to regular SMS messaging. Its not encrypted, but SMS is inherently hilariously vulnerable anyway. For example, 2FA via SMS has long been regarded as a joke/security theater. I don't know the details of why, I think its mainly just because it's ancient.
As for secure messaging, I'd prefer MollyFOSS, if I had need of it and could actually convince any of my friends, family, or associates to care about their privacy and security. Alas, I'm a black sheep in that regard. They prefer SMS and Facebook Messenger. Ugh.