The main focus as a parse healer is getting maximum uptimes on the Z’en & Martial Knowledge debuffs on the specific target (main boss).
You will focus on pushing the group- and your own DPS as much as possible while providing very good uptimes on Combat Prayer and healing in critical situations.
In some setups you might also drop your entire healing, go for a 100% DD parse setup and let your other healer do the job alone. (Yolnahkriin as an example.)
Your goal is to get Max. Magicka + Max. Health.
The best option to run is Artaeum Pickled Fish Bowl.
If it’s too pricy for you, you can also run Blue Food. It really does not make that much of an difference.
IF you really have problems with sustain, go with regen drinks like Witchmother’s, but you should not run into sustain problems if your weaving is good and the group constellation is fine.
The Breton is my personal favorite race for a magicka based healer. He has supreme sustain over all the other classes as well as additional resistances. The lack of Spell Damage compare with the Altmer can be compensated by putting on 3x Spell DMG Glyphs on the Jewelry.
The % calculated cost reduction is simply too strong to be overlooked.
Still a very good race for healers. The Altmer has more Spell Damage than a Breton, but no additional resistance as well as a way worse sustain.