If you add a melted marshmallow to a batch of whipped cream it stabilizes the whipped cream for quite a while. However don't know much about the kosher thing.
An italian buttercream is also a good idea but then you have to do the complicated recipe (which I do every once in a while). However a great shortcut is a butter based butter cream with a jar of fluff mixed in. Delicious, approximates the italian buttercream and no fuss.