If you are looking for easy studies then don't bother with computer science (engineering studies are generally considered not easy, but on the other hand maybe math is your native language).
As for economy studies, the most prestigious in Poland is Warsaw School of Economics, maybe Akademia Leona Koźmińskiego also, but this one is not public.
Wroclaw uni of economy is ok, somewhere at the top of the list also.
I will have to share some times between greece and poland...
It depends but generally lectures usually aren't mandatory, but practise or laboratory lessons are. So it is rather impossible to spend a couple of weeks in Greece during semester.