Can't flash recovery

So I have the AT&T Galaxy S4 SGH-I337 and I flashed a file through Odin and got the bootloader unlocked. If that's what that unlocked lock replacing the bootlogo was supposed to indicate. Then I rooted it, same way, flashed SuperSU through Odin. Then I tried flashing a custom recovery for the phone which seems to be a lot btw. And none of them works, I tried over 30 recoveries none of them work. I tried Odin, flashify, TWRP manager. None works, even tho TWRP has official support for the phone there is no way I can get it working on my phone. PhilZ worked with Flashify but when I rebooted the phone it said "unauthorized software" and would get stuck on the boot screen until I flash the stock recovery back through Odin.

So how am I supposed to get the recovery working? I'm on 4.4.4 btw. And I want to move to CM12.

I heard about Safestrap but also heard that not all roms will work with safestrap. Is that true?
Can I not just flash TWRP through Safestrap and use?