Personally I find the survivability comes from evasion rather than HP/Toughness.
I choose +Power and +Condition damage above all else. I have the health skill which gives +hp per damage dealt. I throw down caltrops when i dodge (a trait) and have the caltrops skill.
Finally, each fight, I use death blossom over and over. I use gain regen+1 initiative every 10 seconds, and stealing = gain 3 initiative. I time my death blossoms based on the opponents attacks. I’ll get at least 4 death blossoms per fight + 2 dodges, which means evading 6 attacks.
If the fight is longer, throw down caltrops and move out of the way as your initiative returns.
Hope that helps.
PS: I’m only level 56, and play exclusively PvE.