Threema is a good option. Not an easy option, but a good one. It uses the Signal protocol, but your private key stays on your device, and you manaage which users you trust to save their public key for communicating with them yourself, including giving three levels of verification for (1) if it’s a random person and you have no way of verifying who they are, (2) if it’s a person whose ID matches someone in your address book, and (3) if it’s someone you’ve met in person and scanned a verifying QR code.