You have about the same health and gear as me, and I have no problem tanking Naxxaramas 10 and most (if not all) Heroic content.
I'd recommend trying to get the Tier 7 Chest and enchant it with +8 Stats or +10 Stats, along with Bracers of the Herald from Ahn'Kahet Heroic, and enchanting it with +40 Stamina.
You've got enough stamina as it is for 10Man Naxx, and maybe 10Man Ulduar (I myself have never been there, but our guild's Main Tank has, and he has about 28,000 health).
Good luck in your tanking endeavors,
90% of raiding comes down to 6 words:
"Don't stand in the bad stuff!"