Indeed, rigging any 1:700 ship is a challenge.
I use the transparent nylon monofilament most of the time, because it appears even thinner than it is. Do NOT use black or white thread- the high contrast makes them look thicker than they are. A medium grey is better.
Every time I use monofilament I swear it will be the last time. The stuff has the flexibility of stainless steel wire :-( Tying knots with it is brutal. But, it looks so great when I finish that I tend to use it next time too.
Model Expo carries some very fine thread (like .007). Most local craft stores do not carry a very good selection anymore. They tell me sewing is in decline.
A well-rigged 1:700 ship is a mark of an experienced modeler and craftsman.