Martha Susannah is absolutely gorgeous - you have to use it if you get the opportunity! It's lovely. Flora Emily is pretty too but there's just something about Martha Susannah that really ticks my boxes.
Felix is nice too although it's not a personal favourite of mine. It works well in the UK and other European countries and will suit a man or boy. I think it's a good choice and has a lovely meaning - happy! 
Asher apparently means happy too so you might want to give that one some consideration too.
If you like Felix, you might also like Finn, Sebastian, Arthur, Alexander, Oscar, Rufus, Caspar, Toby, Orlando, Willoughby, Rocco, Gabriel, Archie, William, Jack, Thomas, Maximilian, Charlie, Tobias, Oliver, Hugo, Rupert, Barnaby, Jasper, Robin, Milo, Kit, Monty, Luke, Rudy, Theo, Edward, Leon, Lucas, Dexter, Amos, Barnabas, Chester, Humphrey, Josiah, Otto, Phineas, Thaddeus, Atticus, Cassius, Cornelius, Magnus, Marcus, Lucius, Maximus, Justus, Julius, Ambrose, Lysander, Louis, Patrick, Silas, Titus, George, Matthew, Bruno, Angus, Max, Cosmo, Fredie, Nico, Soloman, Reuben, Gideon, Inigo, Otis, Sholto, and Rex. But, really, Felix is a fine choice.