I think you mean you're unable to top up your Special Account, i.e. your Special Account has reached the Full Retirement Sum (FRS)? Is that correct?
CPF offers drawdown options starting as early as age 55, so no problem there.
So let's suppose your SA has reached the FRS. You are still able to do the following:
1. You can deposit cash into your MediSave Account as long as the deposit fits within both the CPF Annual Limit and Basic Healthcare Sum (BHS). MA earns 4.0% interest, and this deposit is eligible for tax relief.
2. You can make an "all three account" Voluntary Contribution. This contribution must fit within the CPF Annual Limit. It is eligible for tax relief only if you are self-employed. You will earn >>2.5% interest on this type of contribution, with the exact rate depending on whether your MA has reached the BHS.
3. You can repay OA funds used for housing. The limit is the amount you've used for housing plus accrued interest. These dollars will earn 2.5% interest and are not eligible for tax relief.
4. You may have options involving a spouse or partner.
Options #1 and #2 are very highly likely to beat any/all insurance company sold retirement plans. I'd say even Option #3 is competitive. However, while I think Options #1 and #2 are sufficiently attractive, generally speaking I think regular purchases of a couple low cost, well diversified index funds are more attractive than #3. So that's what I suggest you look into as the non-CPF part of your retirement plan, to make regular monthly buys of a couple low cost, well diversified index funds for the next couple decades. There are lots of discussions about how to do that, and you may decide to do at least some of that via a SRS account, depending on your income tax situation.