PPF is generally not recommended for senior citizens because of its lock in period of 15 years. So, getting interest rates after 15 years, during post retirement age, would not make much sense.
If you have been a prudent investor, and managed to build a good corpus which not only debt and equity assets but also contingency funds, and are not into debt trap of paying any personal loan or education loan etc, you need not bother a lot about how your post retirement expenses will be taken care of.
However this statement will be true only if you have factored in inflation in deciding your savings amount. Concentrating only on the returns will not help you much if you did not factor in inflation. The avenues where you can look forward to invest your funds can be a combination of bank deposits, post office deposits and within MFs, you can go for dynamic debt, and fixed maturity plans. All these put together can give you a good mix of debt portfolio. PPF within the debt stable is not recommended at your age as it locks in your money for 15 years and you can deposit only a limited amount every year.
If you still want to enhance your returns, definitely consider equities. But if you already have a good exposure to equities then you can invest more in MFs where the exposure is currently limited. MFs are more tax efficient both for debt as well as equity. So depending on your expenses and requirements, you can go about saving the required amount.