Like others have said, it will pop out at you and you'll just know. I was trying out names with a fellow FTM for a couple of months before I got my name changed (we would each ask the other to call us 'blah' for the week and see how it felt), and while a lot of the names I chose I really liked, it wasn't until I was reading a book that a name jumped out at me, and I kinda went 'That's it!'
When you find the right one it will click, until then don't stress too much, and go with what feels right, even if someone else has that name already. 🙂