Here are some tips for a general Polish accent. Now the reason I know a Polish accent is because I used to go to a Polish day spa. So my way to crawl into my Polish accent, and to get into the oral posture, is to say exfoliation, exfoliation, exfoliation. It's very similar to your Russian oral posture. So your tongue is pulled back. But it's not pulled back as far as the Russian accent. There's more action in the front of the mouth. Exfoliation, exfoliation, exfoliation.
Some sounds changes for Polish include that ih to ee transition. So "I loved my big trip." in your Polish accent becomes "I loveed my big treep. I loveed my big treep." And it's all very front in the mouth. Unlike your Russian accent. "I loveed my big treep." Same sounds, but you put the focus in a different way and it's more Polish. That th sound, in American English, thin, thick, this, and that, in your Polish accent become theenk, theeck, thees, thaeet. Very far forward. In your Polish accent you'll get a hard R sound. So "Rachels runs errands for her mother and father on Saturday. Rachel runs errands for her mother and father on Saturday." And you still feel all that action in the front of the mouth, even though those R's are pulled back pretty far. Hear how I say the word mother. Mother. Mother. There's no shwa. There's no uh. It's mah. Mahther. Mahther and fahther. Ah.
Try that. And try this phrase. "I gaht ahp, and sahw my fahiles were corrahpt." So the musicality of the Polish accent, feels very reserved to me for some reason. And it feels a little bit softer. A little quieter. But don't take my word for it. Listen to some native Polish speakers, and see what you get from it.