Sure, here goes.
You want to get a pure stam or def/stam (green) gem in your weapon.
Replace the hit gem in your helmet with def/stam to maintain the +12 stam socket bonus.
Gem gloves for expertise/stam in lieu of hit/expertise.
I tend to prefer the +40 stam enchant on bracers in lieu of expertise. As soon as you exceed the 26 expertise mark, you may want to think about replacing your exp chant with stam (if not sooner).
Replace the parry/stam gem in your boots with expertise/stam.
Get either the defense or armor echant on your cloak (be mindful if you go armor that you want to recapture the 540 def mark - def/stam in helmet and weapon may facilitate this).
Epic gems wouldn't hurt either, replace the "rare"s as you can.
All that being said, I'd say you're probably ready for Ulduar as you are. I remember being in a guild that headed into Ulduar, initially, with a max of 10/25 man Naxx gear and doing just fine.