Try the Briar Messaging App

TASK: The Briar app takes privacy to the next level. The biggest advantage is that you can communicate over a local Wi-Fi or hotspot you created and/or Bluetooth. You don't even need to connect to the internet. This has serious limitations but it is the first app that seems to offer this in a good all round package.

WHY: Learning to use new tools give you options if another messaging app gets shutdown or the developers stop work on the project. Having your close family, colleagues or business partners able to use a communications platform that is trustworthy and private can be a huge advantage should Signal get compromised or you need added levels of security that other messaging apps cannot provide. Learn these tools so you have optionality and continue to get better and better.

Here is a good review on Briar: https://dt.gl/briar-new-kid-on-the-messaging-app-block-review/  

Have a look at https://www.securemessagingapps.com/ for the full picture. Needless to say WhatsApp does not score well and even though many people are on it there is a real price to pay in terms of the tracking Facebook do on you.