Hi!
I did composed the music myself. In fact a made a music with lots of instruments but it wasn't working well. So I took the track, removed lots of stuffs and made something more minimalist, and then it worked!
I also made some sfx in a short period of time (bfxr 8bit sounds mixed with real sfxs) but didn't included them because they were'nt fitting the "empty / desolation" mood of the game.
But I believe you are right, good and fitting sfx could improve the game.
Thanks for the feedback, cheers!