kaligoddess: This might help as a reference: http://www.cosplay.com/costume/437189/
I guess it really depends on how thick you want it to be. Arda's are notorious for being much fuller/thicker then most other brands. But yeah, if you feel you're going to want to add in wefts you may as well spring for the Matilda. lol I guess as a comparison, it's much thicker then the CosCom one you posted, but not as thick as Matilda (which is only a slight bit more wefts).