The OP in Krakow, should be able to buy some graded readers there, as well as online from Amazon etc.
there has to be a wrenching away from teaching materials to
The 'Easy Reader' series, and its rivals, aren't usually used as teaching materials; they are mostly intended for self-study (although some courses for young learners occasionally incorporate the ones aimed at kids - most don't). Authentic materials can (and should) be used at every stage of a course, even from day one.
Polish A-Level(s) for English correspond precisely or even closely with Cambridge British Academy standards for A-Level English
Poland has a Matura (rether like Le Bac) rather than A levels.
The British Academy is the UK's national body for the humanities and social sciences - the study of peoples, cultures and societies, past, present and future. It is based in London, not Cambridge and has no role in the various A levels in English; that is a matter for the respective exam boards that offer them.