SMS is not encrypted. Your carrier can read your texts, and in many cases is legally required to produce them on request. iMessage is end-to-end encrypted between Apple devices, which is good — but the moment one person in the conversation uses Android, it falls back to SMS. Green bubble, zero encryption.
Signal is end-to-end encrypted for every message, to every person, on every device. It's open source, audited, and run by a non-profit with no business model that depends on your data. It looks and works almost exactly like iMessage. The switch takes about five minutes.
Download Signal. Set it as your default SMS app on Android (on iOS you can't set it as default, but you can use it for specific contacts). Ask the people you text most to download it too. Once both ends have Signal, the conversation is encrypted automatically — no settings to change, no keys to manage.
The one friction point: you have to convince the other person. This is the only meaningful barrier. For close family and friends, it's worth the ask. For the rest, regular SMS is fine — Signal handles both.
Note on iMessage: if you're all-Apple all the time and don't care about Android users, iMessage is genuinely good and encrypted. Signal is still better (no iCloud backup exposure, better metadata protection, disappearing messages) but iMessage is not the catastrophe SMS is.