Just got to 70!!
The full cobalt set has you crit immune until 72 or 73. You get three tank upgrades during that period from dungeon quests so make sure to get the UK, Nexus and AN quests when you can queue for them (which you already can).
From there continue to look for the crafted tank pieces as you level and you will stay crit immune or very near. Trinkets is the hard part until the upper 70s. Use wow-loot.com to find good tank quest and dungeon rewards. You may need to queue specifically for some of the higher level BC dungeons for trinkets to get you through the low 70s.
"he doens't need healing, he doesn't need healing, he doesn't nee-WHAOSHIT!wtf was that man!". Please stop leaning on TDR. -Teng