SMS for 2fa is deprecated here because of insecurity and TOTP is generally preferable. Can you use that instead?
My first choice is a YubiKey, second choice is the Aegis Authenticator app, and the phone I only use for services that force me to. A few still do, unfortunately!
I understand about DIY and am interested to hear how this goes for you. I might like to try it myself.
If I manage to set up something that I think is interesting and functional enough, I will post about it 😄