I think a cold wallet would be enough to increase the security. On one condition, to use an off-line dedicated computer for this reason. An old laptop would be perfect. Alternative you can use a Raspberry Pi as a cold wallet. It runs Linux you can run all kind of wallets you want and when you are finished, just remove the micro sd card and secure it in a safe place. It's cheaper than any hardware wallet.
Thanks for the share. Quite shocking how easy it is to pull off private keys. All the more reason to switch to a hardware wallet.