You don't mention your character level, and what your skill bar has on it. I mention this because it's the total build that creates survivability, not just the weapon you're wielding. It takes more than just damage dealing to manage mobs.

I think that the basic principle is that you use CC and AoE abilities, especially stuns, blocks, and interrupts, to keep your opponent from attacking you while you deal damage.

If you post more details about your build, someone might be able to offer more specific help.

I did great as a caster in beta with full light armor/no points to health. I hit adds with rune prison and used an ice staff.

Since u said u were a healer with a destro staff I'm assuming u're a templar? If u want to be a dedicated healer that is great, but for leveling up and for playing solo it's much easier if u balance out u;re build a little bit from just a pure healer. This won't even mean u'll have to respec later either since there are so many available skill points in the game-don't feel like u can't master the Restoring Light Tree just because you have skill points invested in the other 2 skill trees.

I have a templar that I put a skill point in each skill tree 1st thing. This allows you to level all three skill trees all at the same time. Don't let those skill slots g to waste. Right away this gives u Radial Sweep, Sun Fire, and Rushed Ceremony. Find yourself face to face with an enemy in a melee situation? Hit them with Radial Sweep. R u facing multiple enemies? Snare them with Sun Fire. Sun Fire also has great range and later u can morph it to hit/snare multiple enemies. And of course u can use Rushed Ceremony for an emergency heal.

R u running out of mana? Templars go through tons of mana so u might want to consider making your main weapon or have an alternative weapon be a stamina consuming weapon(not destro staff or healing staff). Bows are great because u can keep u're distance. I love my bowplar! Keep in mind that later at level 15 u will need to be skilled in 2 weapons. U can level 2 weapons easily by having u're main weapon and then leveling another weapon by equipping it just before turning in completed quests. That way by level 15 u'll be all set to go.

You didn't miss the starting island did you? I did that and missed out on some easy early leveling which put me a couple of levels behind the mobs I was fighting in the first quest hub..

One other suggestion is to use heavy for your 3 main pieces of armor. The other 4 pieces are plenty but will not overcharge the abilities gained if you take all of your light armor skills at higher levels. 5 will over charge them. You can use the three main pieces to get a nice boost in armor rating as well as take advantage of the heavy armor line as well if you wish.

EDIT: I should state that this was with my breton character have not verified with others.