How about a -bel name, eg Isabel, Annabel etc, or just Bella? Then you can keep the Tinkerbell nickname! Annabel Rose is lovely. Or Wendy (on the Tinkerbell/peter pan theme...)
I wouldn't discount Felicity just because DS has a problem with 's'- surely he will grow out of that? And Suzannah- I don't think it matters that your sister has a similar name, she will be flattered, surely?
Other suggestions- Tess, Eliza, Polly, Martha, Zara, Julia, Rowena, Juliet, Rosie, Evangeline, Charlotte, Clementine, Lorna, Larissa, Freya, Phoebe, Lucinda, Rebecca
Let us know what you finally pick!