Wool Cloth
Wool is the next cloth after Linen and will drop from any humanoids between the levels of 16 to 34. You are able to find a lot of wool from just killing humanoids within the level while questing but in this case I recommend running through dungeons. One of the best dungeons to find Wool would be Shadowfang Keep at Silverpine Forest, this instance is highly recommended for the hordes. For the Alliance there is a closer and safer alternative to find wool, Stockade is located within Stormwind City and has plenty of humanoids that will drop bagloads of wool.