Good standard:
Ibis Old Town
Ul. Muranowska 2
00-209 Warsaw
+48 22 310 10 00
H3714@ACCOR.COM
https://goo.gl/maps/Lm9skUsiqs72
Budget options:
DREAM Hostel Warszawa
ul. Krakowskie Przedmieście 55
Warsaw
+48 22 419 48 48
warsaw@dream-hostels.com
Puffa Hostel Lux
Ul. Karowa 31
00-324 Warsaw
+48 22 255 70 88
+48 535 55 08 55
karowa31hostel@gmail.com
http://www.puffahostel.com
https://goo.gl/maps/JS9h569SZ9u
Feel free to book any hotel or hostel from available accomodation websites. Anything around “Stare Miasto” (Old Town) will be close to the coference venue.