Po prostu is always used. It means simply.
Related:
1000 (or more) MOST COMMON POLISH WORDS - (Frequency list)?Does anyone know where I can find a frequency list of the most common polish words? I've looked and can't find any.
The best one so far was 200 words :(
Help would be greatly appreciated!
pl.wiktionary.org/wiki/Indeks:Polski_-_Najpopularniejsze_s%C5%82owa_1-1000
78.9.31.5/server1/lista-frekwencyjna.pdf (beware, this one is 10 THOUSAND pages long and totaly user unfriendly)