Guardian Templar Mystic, Wizard Troubadour Illy. Still sturdy but now not invincable anymore.
IMHO - you now have the ultimate healing duo (some ppl slot in a defiler instead of the mystic, just depends on what you are after spellwise and on what tank you use - you've already got the mystic so no reason to stop using it)

Both healers have group heals/proc/wards if required - but in all honesty - if the MT keep aggro, the need to heal the group will be kept to a minimum

Just to check - you have set all your heals as macros, yes?
- /clearallqueuedabilities
- /cancel_spellcast
- drag whatever healy spell you want into macro

This way you will get a heal when you need it as opposed to putting the heal in a spell que (don't spam the heal key or you'll keep cancelling the cast!)

As a extra confidence booster if your still unsure you can do what I do, I set all my heals up exactly the same - meaning - I hit a key which tells both healers to fire off the small heal, nother key = 2 x big heals, etc etc

The way I think of it is this way - I get both healers to shoot off a small heal, 2 x small heals = something close to 1 x big heal but for a lot less mana at a higher cast speed (most times) - an added bonus is the smaller mana cost is spread over 2 casters meaning both will have plenty in reserve

..and if your still worried on big pulls - IMHO...always....ALWAYS....pre-ward (group ward + group proc pre pull is your friend on big pulls then lay on the single target wards/procs once the tank has aggro)