To answer your question directly, the safest Singapore dollar denominated investments in Singapore are as follows:
#1: Yes, CPF, in its traditional form (not in the CPF Investment Scheme). It’s the absolute safest because it’s guaranteed by the AAA-rated Singapore government, operated by the same government, well protected against the world’s court judgments and creditors, and tax advantaged. There is no greater Singapore dollar safety available.
#2: Singapore Savings Bonds, other Singapore Government Securities (SGSes), and Singapore dollar deposits in banks in Singapore as long as the deposits are below SDIC limits. The bank deposits can be current accounts, savings accounts, and/or fixed deposits.
#3: Agency bonds. Singapore doesn’t have many of these, and they tend to be high denomination and difficult to access. But, for example, Temasek’s general debt obligations are quite safe. Note: NOT the recent series of “Astrea” securities which are not Temasek guaranteed.
The safest investments are also generally the lowest yielding and thus largely inappropriate for young adults saving for retirement (except for emergency reserve fund purposes, and for saving for other purposes). CPF is a unique exception. It’s the #1 safest and also unusually high yielding.