At Lvl 20 take Anti-Magic Shell against spell-damage, if minimal spell damage, take Legion of Northrend.

At Lvl 16 take Frostmourne Feeds if you're getting low on mana for extended trades or chase-downs, if you're doing fine on mana, take Remorseless Winter.
At Lvl 20 take Absolute Zero if the enemy has some ranged you wanna get to. If it's not important to reach their backline, take Death's Advance.

At Lvl 7 take Rune Tap for longer trades. Take Icebound Fortitude for short bursty trades, and the possibility of de-engaging.

At Lvl 20 take Legion of Northrend for more self-healing in-case of short/bursty-trades, take Death's Advance if you can survive without the self-healing.