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.
A black woman's fro is worth a million words- adthomas