Соня

Is Sonya spelt Соня or Сyнья? I've seen it spelt both ways but am not sure which is correct.

Also, are there any more diminutives of Sophia?

Соня of course
Сyнья looks awful, nobody say that.

Or Сoнья? Because wouldn't Соня be pronounced SoNEEya, which doesn't sound as nice as Son'ya?

Соня. Pronunciation - http://mhost.eu.org/tmp/sonya.mp3
Сонья sounds bad.

Ah, thanks. Muchly appreiciated! :)