Provisional License Question...

So DVLA finally sent me that little form that you have to send in with ID, and I think I'm having an idiot moment.

I should be fine to just send in my passport, correct?  Nothing else?  There's space to send 2 documents, but I don't know what else I would send except my US license, but I don't really want to be without both of those.

Also, since it's an up-to-date passport, I don't need anyone to sign the back of my photo, right?

Thanks in advance for helping me through my brain lapse!  

ETA: And did everyone else use this tiny envelope they sent?  It doesn't really seem secure to send my passport in.

I had an up to date passport and still sent in a signed photo--I believe it's more to prove that you match your passport than anything else. I also printed it off online and posted it myself, so I used my own (sturdy) envelope. I don't remember sending in anything more than my passport, though.

I sent in my UK passport, and a passport photo (unsigned). Should be all that's required.

Okay great!  Thanks!