Are there other types of corporate loans or bonds that are low-risks, other than Singapore Savings Bonds since the interest rate is quite low?

You can consider bond ETFs like A35 (AAA-rated government bonds) or MBH (A-rated Investment Grade Corporate Bond) which are relatively low risk. Do note that these products are not capital guaranteed.

CPF is one of the best around. Why not seek to understand CPF first for retirees? A bigger payout is more sustainable with a higher lumpsum imho.

Or annuity plans (but less liquidity).

But if you are an accredited investor or ex-FA who can do claims, then can consider 2nd hand insurance policies that give potential 4% returns, and 2% gauranteed returns. Because there are some inherent risk which retail investors may not be able to resolve.