A mousse differs from a Bavarois in that it usually contains stiffly beaten egg whites. Any Bavarois can be turned into a mousse, but the reverse is not true.
Make Bavarois. At the time the whipping cream is added to the partially set Bavarois, whip the egg whites and salt until starting to get stiff. Then sprinkle in the sugar and beat until whites are very stiff. Fold into the Bavarois mixture alternately with the whipped cream.