Fine and thin are two different qualities--texture and density.

I, too, had dense hair when I was younger. Age, thyroid and a medication I take have thinned it out.

The best way to choose ingredients is by hair properties. Look for others with similar hair and see what they like. It's the best place to start.

My hair has always satiated on products. Even back in my shampoo/conditioner only days. I always rotated products. I do at least one PT a week and use a lot of products with protein.
3a (Corkicelli), highlighted, fine, low porosity

HGs: Anything Sevi; Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; UFD Curly Magic; Botanical Spirits Jellies, CJ Repair Me, Aloe Fix