1. Use mobile phone.
2. Use the most reliable wallet available for mobile phone.
3. Use your mobile phone only as container for your wallet, do not use it for other things such as for phone calls, sms and especially opening websites or mining bitcoin.
4. Only turn on your mobile phone when you want to use your wallet for trading, sending, etc so when you don't use it then just turn it off. Use password protection on it so that when you turn it on it will ask for password that only you know.
5. Store your phone on an iron box or other secure box container, do not bring it with you and if you need a mobile wallet then just make a secondary wallet with the same tips here but with the exception it only have bitcoin with just the amount of you need for buying things, do not bring your main wallet with you where all your bitcoin stored.
It is good to be vigilant but donesn't meant becoming paranoid.
Buyinga hardware wallet like nano or ledger can be safer and cheaper in the same time than buying a smartphone and disable all its features.
You can also store your Bitcoins in different wallets, thereby, if one of them get hacked you don't lose all your money.