A mimosa is a cocktail most similar to which of these drinks?

The Buck's Fizz is a similar type of cocktail as the mimosa, invented a few years earlier in London, which has twice as much champagne as orange juice.

A mimosa cocktail is composed of champagne (or other sparkling wine) and chilled citrus juice, usually orange juice unless otherwise specified. It is traditionally served in a tall champagne flute at brunch, at weddings, or as part of business or first class service on some passenger railways and airlines. The mixing ratio of the "classic mimosa" differs based on the source.

The cocktail is named after the yellow-flowered mimosa plant, 'Acacia dealbata'. The combination of sparkling wine and orange juice has been consumed for centuries in Spain, especially where oranges and cava and other sparkling wines are plentiful, for example in Valencia, Castellón, Alicante and Catalonia. Sparkling wine was also consumed with the juice of apples, grapes, and other fruits.