When you want to use a particular item in 18th century living history, you must first establish its existence and availability. IF you find that it is possible that your persona could have come in contact with such an item, then you may have a precedent for using that item. For instance, in the case of the hammock, were you once a seaman? Did you travel on a ship & use a hammock? Where else might you have seen a hammock in use?
Carrying a covered hammock, Bahia Brazil 1712-1714
Indias 1535 ad.
Slaves carrying a hammock. Brazil 1630s
Jan Van Der Straet's "America" 1600 ad.
Pirate Jean Lafitte sitting in a hammock.
Edinburgh Castle, 18th century (a living history reproduction of hammocks used in the castle).