This insect is about 0.5 mm in length, so it is very small. It doesn't have legs I don't believe, I am not too good at this but I don't know if it's a worm or more like a cocoon for something.
I do find this alarming because I found this one underneath my bed sheet on the mattress. Now I do recall seeing something similar on the crack of the shaky tile floor, so I can't tell if it's just an apartment pest or it actually lives in mattresses.
Any help in identification would be appreciated. Thank you.