Investing in the Polish stock exchange is probably the best you can do. It is true that a non-trivial part of the Polish economy is controlled by foreign companies but these tend to be large international companies so you could invest in them but only into the global company and not just the part of the company that covers Poland.
As a random example, look at supermarket/ retail chains (source). The biggest ones are Polish (although some of them may also have stores in other countries) but Lidl, Aldi (Germany), Netto (Denmark), Spar (Netherlands) or Carrefour (France) are also major players on the Polish market. Of course you can invest in any of these but you can't specifically invest only into the part of them that covers the Polish market.