SimpleX over Tor seems to me like top notch security. With a self hosted SimpleX server that is For only, you of course require your communications partner to also use Tor
Discussion
Even better would be to seek i2p integration for nostr:npub1gsunl7x2y8ka4rn72y9zmzh0j8ntw8ln3956dxe4vg2mldpt4svsuzfy6l.