Terri, with all due respect, she's talking about the mandatory contributions to ZUS. It doesn't matter what private insurance you have, you are obliged as a self employed person in Poland to pay for health insurance via the NFZ.
I'm still confused: Yesterday I went to the insurance company PZU, and they have the insurance "PZU Travels" which insures "foreigners for whom Poland is not the country of permanent residence".
Essentially, you're mixing two things up. While that PZU insurance is absolutely fine for those just living in Poland, self employed people are obliged to take (and pay for) public health insurance, just like employed people.