I have fine, low density hair, too. IMHO, when you don't have a lot of hair, shorter is better. Because of thyroid issues and a medication I take, I've lost a lot of hair. I've worn my hair in an inverted bob for the last four years and I really like it. When it was shoulder length, it looked "stringy." Now it looks "fuller."
Knowing your hair properties is really the best way to pick identify ingredients/products. Here's a link Live Curly Live Free - Curly Hair Basics
Once you determine yours, look for people with hair like yours and see what they use. It's the best place to start.
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
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