Maintenance for the week of December 22:
• [COMPLETE] NA megaservers for maintenance – December 22, 4:00AM EST (9:00 UTC) - 8:00AM EST (13:00 UTC)
• [COMPLETE] EU megaservers for maintenance – December 22, 4:00AM EST (9:00 UTC) - 8:00AM EST (13:00 UTC)
Go for the Thief Mundus stone to increase your spell critical chance. It will increase your critical heal -- and damage, but you are a healer, and the most important thing for you is healing, restoring ressources and buff/debuff, even if you have to help with the DPS when you can.
Legendary quality staff will give you another ~200 spell power, and legendary Jewellery glyphs will give 174 spell power each. Spell power is roughly as important to healers as max magicka. As a Templar we can easily increase our spell power by 25% in combat (minor & major sorcery). Just don't let your regeneration suffer. As a healer you don't want to run out of magicka, though healing harder means you have to heal less, etc. So it's a balance.
Sanctuary has a very small radius, think about 10 meters so you have to ensure your group is close to you. Which is not always possible when you're pugging and your DDs run around like headless chicken. If you want extra spell damage I'd go for worm cult as the 2 piece bonus gives extra spell damage and the 5 piece bonus comes in quite handy. The healing mage is also a nice set.
Worm's Raiment Set and Spell Power Cure Set is a good combination. Using two staves that will give you one piece left over. Ensure it's a head or a shoulder piece, and then you can equip any number of monster set pieces, to suit the situation you're in. For example, Molag Kena if you'd like more Spell Power, or Grothdarr if you'd like more Magicka, or Nerien'eth if you'd like more health, etc etc. The one set piece bonuses from monster sets in this situation are great, and can provide simple flexibility if/when needed.
Don't forget about Twice-born Star and Julianos. Both those tick many boxes for what healers need too. I still have my old healing set of Twice-Born Star, Martial Knowledge and Willpower; and it still works great.