I'm looking for info about the poland country/region please! if you can direct any english sources my way that would be awesome.
As it so happens, I do have a collection of English resources bookmarked on Polish mythology and paganism because of an old Polish colleague of mine.
If you have specific questions, I would defer you to @slavicafire as not only is she Polish herself but she is quite well-versed and well-educated on the topic. You could also search her blog as she has quite a few posts on the Old Gods within the context of Poland.
Bear in mind that many of these resources speak about different regions and compare them in their analysis and quest for greater understanding of Slavic mythology and its diversity. However, some specifically address Poland.
My dear readers - feel free to add any sources that you use within the comments.
Tales by Polish Authors by Henryk Sienkiewicz, Stefan Żeromski, Adam Szymański and Wacław Sieroszewski
Slavic Folklore, A Handbook by Natalie Kononenko
Forests of the Vampires: Slavic Myth (Myth and Mankind) by Charles Phillips
An essay on Slavic Paganism by Irina Yakubin and Mariya Gershkovich
Gods of the Ancient Slavs by Myroshlava T. Znayenko
Polish Folklore and Myth by Joanne Asala
The Archaeology of Early Medieval Poland by Andrzej Buko
The Slavs by Marija Gimbutas
Slavonic Pagan Sanctuaries by Leszek Paweł Słupecki
The Gods of the Ancient Slavs by Myroslava Znayenko
Coexistence or Conflict? The Problem of Dual Belief in Polish Folklore by Anna Brzozowska-Krajka
Late Pagan and Early Christian Poland by Jerzy Gąssowski
Rituals in the Past edited by Leszek Gardeła & Agnieszka Půlpánová-Reszczyńska
The cultural unity of the Slavs in the Early Middle Ages by Witold Hensel
Saxo Grammaticus on Slavic Pre-Christian Religion by Stanislaw Sielicki
Slavic Protective Magic in the Early Middle Ages on Polish Territories by Joanna Wawrzeniuk
Studies on Religion: Seeking Origins and Manifestations of Religion (see the section on Slavic folk beliefs) by Joanna Popielska-Grzybowska,& Jadwiga Iwaszczuk
What is known about Slavic mythology by Mikołaj Gliński
Slavic Daemons: The Good, the Bad and the Ugly by Marek Kępa
Roots Revival: How Slavic Faith Returned to Poland by Adrian Sobolewski
Wikipedia, which is highly inaccurate and encourages a black-and-white worldview.
Dmitriy Kushnir. His work is mixture of New Age, unverified information and non-Slavic beliefs that mirror his personal worldview. His works are also incredibly racist and sexist.
The Book of Veles, which is highly controversial in terms of authenticity. It is considered to be a nationalist forgery by many folks.
I hope that this gives you a good place to begin your research.