The big problem with buying an annuity (beyond the potentially high fees and lack of inflation adjustment of benefits) is that you give away liquidity for what may need to be a large portion of your nest egg. You also reduce your bequest, potentially by a lot.

Regarding flexible spending plan, that's probably the best course of action. As I discuss here: https://medium.com/financial-strategy/your-single-best-way-to-avoid-running-out-of-money-in-retirement-a9793e0eb5cd.

If you start out with a 4% draw like the 4% rule, but dynamically adjust your draw each year the market soars or crashes, respectively, you can reduce your risk of running out from over 13% (fixed 4% rule) to less than 0.1%!

And the beauty of it is that even if you need to trim 10% from your draw in a given year, given that you have other sources of retirement income (e.g., Social Security), that may only require a 5% reduction in your budget for a year or two until the market recovers.

Other good options include transitioning into retirement gradually, and investing in income-producing assets like rental real estate.