What is the softest stuffing for a pillow(for my gecko)?

So my gecko recently too a fall and Y!A ppl said to put him on a pillow and be calm around him. I want Rafiki to have the best so i'm home making him a pillow and want to know what the best substance to put in it for maximum softness. It's not exactly urgent but I want to know today. 10 pts will be rewarded. thanks ;)