Bear in mind massage alone can promote growth. These two authors always consider the science

THE NATURAL HAVEN: Clear Castor Oil or Black Castor Oil - What is the Difference?
THE NATURAL HAVEN: Myth or Fact : Can Castor Oil Really Thicken Your Hair?
Castor Oil and Its Derivatives
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