IMO all that bleaching has probably fried your hair. I think products and CG techniques may help some but I doubt the double bleached hair will ever be the same. Not sure how you feel about short hair but If it were me I would start transitioning and get at least a few inches cut off to make it easier. I know that is hard with bleach blonde hair and dark roots. Dying the hair dark will make transitioning easier but it won't repair your hair. I am no expert on dyes because I had a few bad experiences with permanent dyes and vowed never to touch it again. Going blonde once dried my hair out and broke it off. Maybe you could do a semi permanent? Im not sure about henna on bleached hair. Chemicals increase your porosity so yours is likely high right now. Good luck.
"More people would learn from their mistakes if they weren't so busy denying them." - Harold J. Smith.