I think Ruby & Ashley are different enough that it doesn't matter. If his name was Reuben I might rethink Ruby but otherwise I think it's fine. Ruby is very pretty. I've only met one Ruby & she was just gorgeous.

ETA: FWIW, my brother, sister & I all have names ended in an ee sound.

Some suggestions:
Erin
Isla
Adele
Jenna
Kaylin
Claire
Hazel
Talia
Milla
Amelia
Mabel
Jasmine
Estelle/Estella
Eloise
Jane
Caitlyn
Elizabeth
Kyra