Phineas - not keen, sounds quite pretentious
Finnian - okay, prefer Finn or Finlay
Monte - Only seen it spelt Monty. It's quite sweet. Montgomery for formal?
Rafferty - Doesn't sound like a human boy to me. Not a British one anyway
Charlie - like it. Would christen Charles
Leo - like it
Archie - like it
Felix - really like it
Oscar love it. One of my favourite boys names
Girls
Bella - pretty. Would use Annabella, Arabella or Isabella for formal version
Minnie - don't like it. In the words of Ross Geller 'you say Minnie ... you hear mouse.'
Jemima - like it
Felicity - love it
Poppy - it's ok
Beatrice - not keen
Similar boys - Alfie, Andre, Benedict, Caspian, Cosmo, Frederick, Gabriel, Henry, Jefferson, Luca, Leon, Marcus, Nathaniel, Owen, Preston, Quinn, Raphael, Theo, Zachary
Girls are harder as I would say Minnie and Poppy are at the opposite end of the spectrum to Beatrice but how about:
Alyssa, Bianca, Chloe, Daisy, Eloise, Francesca, Gabriella, Heidi, Isla, Jessica, Katie, Lara, Molly, Nina, Olivia, Phoebe, Rosie, Sadie, Thea, Verity, Xanthe, Zoe