My eldest is a Savannah but I don't either of my other two children's names 'go' with hers (or with each other to be honest). I also have a Jessica and a Xanthe and see the three names as being in 3 different 'groups' really. I have eclectic tastes.
I do think that Savannah and Jaxon go well. Other girls' names that I think 'belong' with them:
Aubrey, Alexis, Amber, Alyssa, Amberley, Bailey, Bronte, Cassidy, Cherry, Christabel, Darcey, Devon, Dulcie, Delphi, Elodie, Emery, Effie, Eden, Fallon, Genesis, Gabriella, Halle, Hayley, India, Jordan, Jasmine, Kayla, Kendall, Kayleigh, Livia, Leonie, Lyra, Mika, Macey, Misty, Madison, Mackenzie, Nikita, Nia, Piper, Quinn, Riley, Romilly, Rhiannon, Rosina, Sabrina, Saffron, Sorrell, Sadie, Sasha, Tegan, Tallulah, Tansy, Verity, Vanessa, Zia