You aren't uncrushable so against bosses you will take a bit more damage than usual but it's the lower HP and armor and avoidance that makes you feel that way and it will improve as you get gear drops.
You need to continue getting your keepers of time rep up so you can get
http://www.wowhead.com/?item=29186 for your head. Once you get that you should be able to equip
http://www.wowhead.com/?item=29276 instead of eternium ring and that will improve as your rep goes up.
You need a fortitude enchant on your wrist
I dont know what you were thinking when you put
http://www.wowhead.com/?item=30566 in your legs but atm it doesnt work you need to replace with a +12 stam or make the bonus work by regemming.
Basically you just need some drops now and keep working it.
To be honest however if I was in your spot I would hit BG's and go get the S2 mace. Couple of days of agony in BG's to get your
http://www.wowhead.com/?item=32963 and not worry about threat again for ages.
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