Kinky Curly Knot Today is the best detangler I've used. I have fine hair as well. My hair is BSL and I use about quarter-sized blob to detangle without weighing down my hair.
I suppose you could also dilute it with distilled water if you find it is too heavy on its own.
CG Journey Start Date: 08.21.12 Now modified CG
F/M texture, Med Density, Low/Normal Porosity, Hennindigo
Current Routine (Still working out the kinks):
Sulfate wash: CHSTS
CO-Wash: IEC, VO5VMT, TNRV
Rinse Out: YTCarrots, DLOO, Renpure Red, GVPCBLI: YTCarrots, CCC
PT: NPF Styler: AG:RC, KCCC, LALNC, FSG