When you are connected to internet you have to be very careful no matter what device we are using,IOS,Android or windows or any other operating system because even reputed softares in the pasts were found that they are tracking user's privacy information.Best solution is hardware wallet.
Now even a hardware wallet does not give any guarantees because there are some cases of hacking start to appear or some kind of inside replacement of address. I think in order to safely store cryptocurrency, you can use some kind of smartphone that will never connect to the Internet. it will be harder to hack it.
Hardware wallets have no guarantee because they can still be hacked and again you still need to keep your private key off the hardware, these hardware wallet can get damaged too so still backing up your private key is certain