David Abulafia, A Mediterranean Emporium: the Catalan Kingdom of Majorca (1994)
David Abulafia, The Great Sea: a human history of the Mediterranean (2011)
Robert Bartlett, Making of Europe: Conquest, Colonization, and Cultural Change, 950- 1350 (1993)
Stephen P. Bensch, Barcelona and its Rulers, 1096–1291 (1995)
Robert I. Burns, Jews in the Notarial Culture: Latinate Wills in Mediterranean Spain, 1250- 1350 (1996)
Steven A. Epstein, ‘Secrecy and Genoese commercial practices’, Journal of Medieval History, (vol 20, 1994, pp. 313-325)
Geoffrey Hosking, Trust: A History (2014)
You should be able to gain free access to the books listed above through your school or local county library service.