Not your keys, not your crypto. Use a nice safe hardware wallet. Just check for extra SIM cards first, and audit the key generator.
The idea that someone would have to buy a hardware wallet to be safe, but first audit the hardware and software is both a but ridiculous and infeasible. Unless one can actually inspect the code running on the device, auditing am open source library online doesn't tell you what is running on your device.
Maybe the sim card is on a timer to broadcast your keys after a year, so you just can't detect cellular signal usage now.
To securely own bitcoin you have to first create a new chip fabrication plant to then make your own hardware wallet.
Keep the seed phrase safe. Use actual dice to generate it. Put a chunk of it into your wallet, a chunk into your password manager, a chunk in your attic or in a book, etc. Never type it into an internet connected computer.
Oh and, never tell anyone about how much crypto you have.
This is reasonably safe, and reasonably within the capabilities of a non cryptography nerd.