What about
Morgana Bellamie instead of
Bellatrix? Nice flow; better associations!
Morgana Tamsin is very Cornish - perhaps that's what your subconscious mind is thinking of! Can't be the -a- sound, because then
Lavender would work too, and I don't really think it does. Ditto
Damaris.
I like
Morgana with
Jean,
Rachel and
Tamsin and would like it better with
Beatrice than with
Beatrix.
Morgan Lennox is definitely stylish!