Preventing heavy top layer of cake from crushing cream layer
To make the whipped cream firmer, you could set it with gelatine or agar (which I think would be better unless the cake is being refrigerated until just before serving). For the recipe, I refer you to http://video.about.com/southernfood/How-to-Stabilize-Whipped-Cream.htm (video).
Having looked at the video, you might even want to add a half more of the gelatine/agar so it is really set (much like a pastry cream in a fraisier).
Also, if a creamy filling is required could a pastry cream be used instead of whipped cream? It would set and cut much better (although would lose the lightness of whipped cream which you may be after - you could fold whipped egg whites or cream into it but then you have the same problem of it squeezing out).