Make sure to get stuff WITHOUT any added chemicals.
Yes, make sure you get floss (polyester quilt batting - it's called at a fabric store) that is unadulterated - no additives, nor fire retardants, etc.
You can get a one square meter roll piece for about $5. and it'll last you a few months.
You might also look into getting some bagged Seachem Purigen for your filter - that will really clarify & polish your water. And a fine mesh pre-filter sponge on your filter intake will help a great deal too. Just rinse it well every few days (takes but a minute).