How to prepare for phone upgrade with manually managed music

I have an iPhone 5 and I am strongly considering upgrading to the iPhone 5s. The trouble is that I have manually managed all of the music on my phone: I dragged and dropped every song I wanted from our iTunes library to my phone. I like to keep my phone private, thus I don't sync my photos, books, or ringtones in iTunes either. There are also a lot of extraneous contacts and such on the computer that I wish to avoid deleting from my phone. How can I retain my information when switching to a new phone?