Try this book for a good place to start when doing research on Singapore. Be certain to read the Introduction to the Bibliography (pages 313-318) and see the bibliography that follows (318-361):
Historical Dictionary of Singapore (New edition) by Justin Corfield
Lanham, Md. : Scarecrow Press, c2011.
Paper Copy: Kroch Library Asia Reference (Non-Circulating) DS610.4 .M85 2011
Online Copy: https://newcatalog.library.cornell.edu/catalog/8377324
Here is an older (1988) but useful research book containing annotated title listings of major and standard information sources covering a large number of topics: