Did the strand tests come out fine? Which specific products do you have from the brands you list?

Unfortunately hair is dead so it cannot be repaired, I would cut off the worst of the damage if your hair is breaking off. Where possible use products at pH 4.5 to 5.5 which will help keep the cuticle flat and prevent the pH rollercoaster further damaging your hair. pH strips are SUPER cheap on eBay, some products are listed on the Natural Haven blog and elsewhere online.

Two key ingredients for breaking hair, first and foremost hardcore hydrolysed protein. Could try gelatin but something like Colorful Neutral protein filler would be better - this is practical because you can basically DIY with it and play with concentrations and combinations so waste nothing. Ingredients that *may* aid penetration include aloe vera, behentrimonium methosulphate (a cationic surfactant, may be a main ingredient in a conditioner you already have) and lecithin.
Colorful Products - Colorful Neutral Protein Filler 4 oz.

Secondly coconut oil - refined edible stuff is cheap - use as an ingredient in a deep conditioner you don't have to use it straight up if that is too much for your fine hair. Forget what you have been sensitive to in the past and don't expect instant gratification, you might have to suffer slightly dry or slightly greasy hair occasionally and do multiple treatments. The excess oil should wash out fine with piles of cheap conditioner tho.

Other beneficial ingredients include ceramides and panthenol. KCKT can be used as an ingredient in a DIY project, there are multiple variations on Kimmaytube's (from YouTube) leave in conditioner online.

Treat your hair like antique lace: ONLY finger detangle no brushing or combing, don't sleep on wet hair that will pull on it when it's in the delicate wet state, be careful when clipping, consider loose protective styling so the ends don't pull on your car seat/ purse strap/ clothing/ sofa, use a satin pillowcase or bonnet at night etc.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect