I will suggest you make use of Electrum and BlueWallet, which are both open-source wallets that are both compatible with iOS and Android.
There is no IOS version of electrum.
Electrum is available on Linux, Windows, Android and MacOS.
To OP:
Both wallets that were recommended by Nwada001 are secure and I also recommend them.
Just note that it's not a good idea to keep a big amount of money on online wallets.