You might want to consider having an ACTH stim
test performed first in order to assess current state of your adrenals. Problem with just doing regular cortisol labs (blood or saliva) at this juncture is that cortisol levels may very well come back low -- not because your adrenals haven't improved...but rather, because ACTH signal is blunted at the pituitary level in light of exogenous intake of cortisol during these last eighteen months.
Should cortisol response to ACTH stim
test be sufficient or good, you can consider weaning yourself off Cortef slowly...
You might also want to have condition of your thyroid assessed...or at least strive for 'normal' temperature readings prior to coming off Cortef...otherwise, over time, you run the risk of reverting back to an adrenally fatigued state.