index fund like Warren Buffett, generally considered the greatest market investor of all time, recommended for people who don't want to spend time learning and following the stock market.
This was advice many years ago. My preference is a Total U.S. Stock Market Index fund, which has averaged slightly better over the long run because it has midcaps and small caps that on average have done better than the S&P 500 (which is large cap), and is somewhat more diversified.
(This post is prompted by some posts upthread that make it sound like it is difficult and time consuming and that you might need some kind of expert for that)
I strongly advise against hiring someone to pick stocks or funds. Most professional active fund managers do worse than their benchmarks and ditto against the S&P 500 and Total U.S. Stock Market indices. So your chances with a rando broker or financial advisor type will more likely than not be even less.
"I am not a person who actively follows the stock market, nor do I really want to"
Ironically, that's a HUGE positive -- it's people who fret about its daily and weekly moves that do the worst, as they are more likely to panic sell when the market dips. Just buy and hold a widely diversified U.S. stock market index fund, and you will do better than the vast majority of the "smartest people in the room" types.
And you definitely don't want to leave out equities
Over the past 20 years, it has grown 6.3710 fold, an average annual increase of 9.7%/year
Over the past 50 years, it has grown 131 fold, an average annual increase of 10.2%/year
and so on.
This is from the below link, which also has similar for bonds, Treasury bills, and gold. These don't come close to matching the increase in equities.
http://pages.stern.nyu.edu/~adamodar/New_Home_Page/datafile/histretSP.html
Simulation after simulation by countless authors and organizations show one is more likely to exhaust their nest egg if it is all in fixed income like bonds and CDs than if it is majority equity. Nothing holds up as well in the face of withdrawals and inflation than does equities, except perhaps real estate. In other words, it's an even bigger gamble to not have a sizable proportion in equities.
That said, being an old person, I hedge by having about 40% of my easily re-investible assets in bonds and other fixed income. On top of that, I have an annuity, Social Security income, my house -- all non-equity investments or sources of income. So I'm far from being an "all equities" fanatic.