It's taken an embarrassingly long time to be introduced, but two-step verification is now available in most regions for the PlayStation 4. To set it up, scroll to 'Settings', 'PlayStation Network/Account Management', 'Account Information', 'Security', 'Two-Step Verification'. You'll obviously need a working mobile phone to set everything up appropriately.
The way this works is that you'll receive a verification code via SMS each time you try to log into your account. It ultimately means that, should your password be compromised, a hacker would need to have access to your phone in order to login to your account, which seriously reduces the odds of them gaining access to your stuff.
It's worth setting up, then, and doesn't take many minutes. Yes, this should have been introduced years ago – but hey, at least it's here now.
Update (11:45PM BST): As mentioned in the comments, you can also set up two-factor verification online through here.