vocal/piano sheetmusic / Easter (Istanbul)

Dear IN members. Who can help me with finding sheetmusic. I am looking for music (voice / piano) to sing on Easter Sunday in church 24th of April but it's hard to find music. I'm not too familiar with what to sing on such an occasion.

I am a countertenor (high alto/ mezzosoprano). The service will be held in the Crimean Church at 10am. Serdar Ekrem sokak Beyoğlu.

Suggestions will be more than welcome. I will sing with church organ or piano.
Hope to hear from you since little time has left. :)