Can be achieved by placing different Expensive style furniture pieces, it doesn't matter what type (can be kitchen, chairs, art) as long as it has the Expensive indicator in the game.
More Expensive furniture will unlock while researching different things at the decoration shrine and you will also be able to unlock some Expensive Furniture via friendship levels and you are able to buy an Expensive 'Fancy Food Bowl'.
The game will state if you already have 1 of an item and that the stats won't go up, i.e.; have 2 of the same Expensive furniture of Expensive: 2 stat, is not 4 stat, it's 2 stat.