My favourite on your list is Beatrix. I love it and would use it in a heartbeat. I can see why you are hesitant to use it, however, given that you already have a child ending in 'x'. This would probably sway me not to use it, too.
i also love Cora and that would be my next pick (Coraline is a great option, too!)
carys is also nice, and Etta is beautiful. I am not the biggest fan of Regan or Sienna.