Shirts and waistcoats will give a bit more of a formal feel whilst sleeves jumpers will provide the same shape but will provide comfort and a bit more of a casual style.
A comparison with Gideon Koppel's stylistically - comparable Sleep Furiously (2008) is illustrative: Koppel's is a work of deep feeling, whilst Bestiaire comes across as more of an icy formal exercise than a frolic with living, breathing creatures.