OK, for what it's worth I've just spent a couple of hours combining alternative spellings of all names scoring at least 100 (ie a manageable set of boys and of girls, at around 400 each rather than the 5000+).
The top tens are:
1 HARRI / HARRY / HARRIS / HARRISON 9,680
2 OLIVER / OLIVIER / OLLIE / OLLY 8,337
3 JACOB / JAKUB / JAKE 8,181
4 MOHAMED / MOHAMMAD / MOHAMMED / MUHAMMAD / MUHAMMED 8,006
5 THOMAS / TOM / TOMAS / TOMMY / TOMOS 6,720
6 CHARLES / CHARLIE 6,659
7 JAC(K) 6,436
8 JAMES / JAMIE 5,720
9 ALFIE / ALFRED 5,218
10 RYLEE / RYLEY / RILEY 5,208
1 AVA / EVA / EVE / EVIE / EVELYN 10,692
2 SOFIA / SOPHIA / SOPHIE / ZOFIA 7,824
3 ISABEL / ISABELLA / ISABELLE / ISOBEL / ISOBELLE / IZABELLA 7,620
4 AMELIA 7,293
5 LILY / LILLY / LILLIE 6,982
6 MAIA / MAJA / MAYA 6,020
7 EMILY / EMILIA / EMELIA 5,393
8 OLIVIA / LIVIA / OLIWIA 4,854
9 JESSICA / JESSIE 4,468
10 GRACE / GRACIE 4,415