I wonder is this enough for decent life in Warsaw ?
It is just enough for a decent life but you won`t put much money aside.
pl.traveltables.com/country/poland/city/warsaw/cost-of-living
Single room
You mean a bedsit or studio flat? Coz both are very cheap now when non-resident uni students have stayed at their family homes during online education. You can rent a nice studio for 1500 plus utilities.
olx.pl/d/oferta/atrakcyjna-kawalerka-ul-andersa-warszawa-super-cena-1500-z-czynszem-CID3-IDJpw6c.html#3cdac4f566