Best defense for Witch?

Whats the best way to improve an Arc Witch's survivability? At level 76 and doing level 66 maps I feel like I am taking huge amounts of damage sometimes especially from physical attacks.
I don't die often but that's mainly because my Zombies are good meat shields. I don't have any armor and my evasion rating is about 350.

3150 life
3100 mana
max resists

Should I buy a Cloak of Defiance for mind over matter? I have no idea how to mitigate some of the damage that I receive especially from some unique map bosses like new Brutus and Defiler boss.

Any suggestions are appreciated.

is what usually use.

I play life shield hybrid usually aiming for 4k life & 4k shield by the time I'm level 70-80.

I'm guessing if you only have 3k life then you must have a shit ton of armor/evasion or another way to mitigate damage.

If you've not got any other form of defense then yeah you will feel VERY squishy in maps with 3k

You seem to have a lot of mana, why not go for the MoM node, the one which makes some of your damage taken come from mana.