Poland improves of OTL with any change that reduces its time under Nazi occupation. It's too late to stop many heinous atrocities and satellitization is pretty much overdetermined.
So, PODs leading to shortened occupation include-
a) Soviet preventive strike against Germans, 1940
b) Soviet preventive strike in 1941
a) and b) have the benefit of providing a short term opportunity for some Polish civilians, especially ghetto dwellers and camp inmates to escape and flee or for the young men to be conscripted into Soviet backed forces.
Many civilians will once again fall behind Nazi lines after the inevitable German counteroffensive, but more will either escape or get a chance to die fighting, the Nazis will be taking serious losses earlier, the Germans will capture fewer resources from the Soviets intact, and the Soviets will have a better territorial position for all later campaigns, shortening the lifespan of the war and the Nazi regime and the occupation of Poland. (Even with quite poor performance by the Red Army, followed by a strong Nazi counterattack, and Soviet retreat, the front-lines throughout ATL 1941, 1942 and 1943 will be west of OTL's 1941, 1942 and 1943, and the Soviets will probably be able to use more of their infrastructure in place rather than having to evacuate (especially in places like the Donbass).
Of the two, a 1940 preemption is probably better because the Germans are less strong in terms of alliances and military presence in the Balkans in comparison with 1941. This applies even USSR tactical performance is suckier in July-December 1940, than in Jan-May 1941.
OK, so this dials back the annihilation, but does satisfy the OPs condition of avoiding becoming a Soviet satellite.
PoDs to ensure against satellitization depend on the Soviets not reaching some or all of Polish territory. So, Nazi victory over the Soviets, collapse of the Soviet state and war effort, or other things that slow down Soviet counteroffensives like unabated command irrationality, no Lend-Lease or more flexible German defensive postures in the east, or a US-UK Japan first strategy and corresponding reduction in their actions to the south and west could possibly keep some or all of Poland under Nazi occupation until after the WAllies have atomic bombs raining down on Germany. An atomic bomb induced surrender could have the WAllies dictating the disposition of most German occupied territories. (As was the case, at least initially, with the Japanese surrender in Asia).
The problem with longer Nazi occupations of Poland is that it increases the time the Nazis are annihilating the Poles (of all religions) as you mention in the OP.
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To have the western powers get boots on the ground in Poland before the Soviets do, requires more exotic PoDs, like -
Germany forcing America into the war in 1940, failing to enlist Japan as an ally and still picking a fight with the USSR on schedule.
It's crazy but not as crazy as it might sound. With the Fall of France accomplished, (and small size of American air and ground forces), Hitler need not be concerned about the American army. He may entertain naval operational arguments that maximum scope for U-Boat operations against British lifelines is worth the cost even if the Americans enter the naval war as an immediate consequence.
Follow that up with an Arctic/North Sea strategy of initial ops against German occupied Norway instead of the Med, while building up for an earlier Overlord, and you get more of a shot of WAllies being the first in Poland.
Granted, when the Germans begin to lose in the western fronts they'll begin to trade space for time in the east. But the finish-line need not be exactly where it was in OTL 1945.
This is especially so if the Arctic-North Sea front starting with Norway draws Sweden into the war (involuntarily) and leads to an eventual Baltic campaign. After a year or so campaigning in Sweden the WAllies can reclaim it to the Baltic coast and present a threat to northern Germany, Denmark and Poland, and are at jumping off points to move into Poland and to support the Home Army.