You did give some criteria, which does sorta narrow it down - but not much. Not nearly as much as you might think.
Security is what you do, not what the OS does. Regardless of the distro you choose, you will be the weakest link in the security chain. (This is true for all of us.) Security is a process, not an application.
So, next on your list is simple. Simple for you means something different to me - and to the next person, and to the next person. We don't know how you define simple or what you are capable of digesting or what how long it will take you to learn.
With that in mind, I'd recommend this link:
Finally, an attempt to answer to the age old question: Which Linux distro is the best? Read on to find out which distro is the best Linux distro.
linuxtips.gq
Do you want to go with something that looks familiar to a Windows user? Do you want something that looks more like Android? Do you want something that works out of the box, or do you want to customize everything? Do you want to have as much opensource software as you can get?
The list of questions is endless. This question will likely get you answers that show you their preferences, and that's absolutely okay - but they'll be telling you what worked for them and you should find what works for you.