The "easiest" way - although one of the more exptensive is to buy this.
https://www.amazon.com/Micro1v8-2-Pa...rds=jim.sh+usb
"Jim.sh" had made a board that you could buy in 5v, 3.3v or <floating based on vcc in> configurations, but he has stopped shipping those to amazon.
Then he made this default 1.8v version ( 3.3v with jumper ), but he only sells it in a 2-pack.
Its small enough to leave inside your kindle permanently too. knc1 has a post where he did that, and a few other people.