So you need 3 legendaries to do this:
1 - the follower tokens that says "your follower cant die"
2 - a unity ring equipped on your follower
3 - a unity ring equipped on yourself
That's it , you now take 50% less damage - works in hardcore as well.
Again, I don't think it is intended and there is a big chance it will be nerfed soon so use it while you can.