No-one was thinking in terms of the Oder-Neisse line in 1919. Not even the wildest, most unrealistic Polish nationalists.
What might happen is for the Czechs to get all of historic Silesia as they wanted and for Poland to get the pre-partition border and to get the plebiscite areas in East Prussia assigned to them outright (the Mausurians in the South of East Prussia were Polish speaking, but due to being Protestants they felt themselves more German than Polish which is why they voted to stay part of Germany IOTL).
Also, while we are talking about land people didn't want - the Danes would not want all of Schleswig-Holstein - they saw it as being too German.
While the new nations in the East are getting all this land, France must certainly get more of Germany - at least the Saar would become French, possibly the whole of the Rhineland (though more likely it would become an independent state allied to France).
Getting back to Prussia, I have a hard time seeing Prussia separated from Germany even in a max-Germany screw. What might happen is that Prussia declares independence from Germany - there was a plan to preserve the Eastern parts of Germany by them declaring independence and then telling the allies with a sincere face that they really weren't a bunch of German army officers and junkers trying to preserve their power. The plan does not seem to ever have been taken seriously and I have a hard time imagining a TL in which it might become so.
The allies did consider breaking Germany up after the end of WW1 - a TL where this happens might lead to an Austro-Bavarian union, but I don't see it happening directly. More likely, Bavaria would be made independent, Austria is reduced to a rump, then, as Prussia recovers its power in the late 20s, France and Britain start to change their policies in Central Europe, and when the Great Depression hits, things have changed enough that the pair give their blessing to an Austria-Bavaria union (the depression saw an upsurge in desire for Anschluss IOTL, so I'm assuming something similar happens in this balkanized Germany scenario).
fasquardon