Remember you can always pop a humanity in a pinch if you run out of flasks, that will completely refill your HP bar, it will also give you a small bit of extra damage since liquid humanity scales up the damage of chaos weapons.
If you want to play with a little more of a safety net you might consider swapping out that grass crest shield for an eagle shield, or putting it on your alt off-hand and switch to it when you start fighting Super Ornstein. It offers 95% protection against physical damage and 75% protection against lightning. Though it weighs 6 units (3 more than grass crest) so it will probably screw up your ability to fast roll without some armor sacrifices.
I personally don't think it's worth burning twinkling on silver knight armor, but if you think you're going to use it long term it would be a good investment.