Clara - I like it. Sweet, pretty and classic. I don't think it's all that popular Louisa - It's ok. Not overly keen and, like you, I don't like Lou etc
Helena - not keen
Martha - really like it
Georgina (Georgie) - love it
Sara - quite like it, especially pronounced Saar-ah rather than saeh-ruh
Tess - not keen. It's a bit short and hard to my ears.
I'd definitely go with Georgina from your list, with Martha as a second choice.
Other names in a similar vein:
Annie, Agnes, April, Alice, Bonnie, Beatrice, Constance, Clarice, Cecilia, Claudia, Clarissa, Daphne, Dorothy, Delilah, Emma, Evelyn, Erica, Esther, Eleanor, Frances, Florence, Gabriella, Hannah, Harriet, Henrietta, Iris, Ivy, Josephine, Juliet, Julia, Joanna, Katherine, Lydia, Lois, Mary, Margaret, Madeleine, Miriam, Nancy, Nadia, Phoebe, Polly, Rebecca, Ruth, Rachel, Rose, Sylvia, Susan, Susannah, Tabitha, Violet, Verity, Victoria