You're just not searching in the right places. In woven textiles, weight or face weight is always known by someone. It isn't the only parameter, but it is a valued one.
You are chasing a chimera because as the wool become lighter -- think the finest suitings, or what with interest in water-shedding, scarves -- it becomes more fragile, lacking in tensile strength and toughness, not to mention being subject to snagging.
As a practical matter, the easiest and least expensive shield and cover of the UQ for backyard hammock use may be an inexpensive hammock like the Grand Trunks polyesters, selling last week for $100/8, and this week for $2 more. Adjust once with a knotted cord the effective length to the hammock bearing an UQ, attach a pair of mini-biners, and call it a day, letting dew and fog collect on that second hammock instead of on the UQ and main hammock, and letting you put those away immediately for next use after you unclip the cover in the AM.
This rider is all for wool, especially contemporary treated stuff for use as base layer. The 4lb Irish fisherman's sweater in raw wool? Not so much. Alpaca blankets in cold mist and rain? Only with llama's to carry them and coca tea to shed hunger and cold at high altitude.