I have no voice, yet I unlock secrets. I have a single eye, but I am completely blind. What am I?

I’m light as a feather, yet born to begin,
 a delicate thing that lets warmth enter in. I’m gathered for when the weather turns cold, taken from nature, quiet and old. I need only a spark, a flicker, a glow,
 and suddenly light begins to grow. I can be kindling, yet mostly not quite,
 a glimmer of hope in the dark of night. 
 What am I?

A drill bit with an indestructible core... A luxury forever more.

Q: How do you make a water bed bouncier? A: You fill it with...

My first four are a tiny thing you take for better health My last four are what Sherlock cracked to build Sir Doyle's wealth In the middle lies the profile best to keep for stealth Together, cover soft and clean you nestle to yourself