Home Forums Thread Like Summary - Upgrade OS or replace iMac?

This iMac I'm typing on is apparently 2011 running 10.9.5 = Mavericks.
Twice in the last couple of months it has switched itself off. (no power cut). The latest was about a week ago. When I powered it back up (phew!) it said words to the effect of "something wrong with your operating system", which set me on a hunt, and to this forum for suggestions and help.

It seems I could either upgrade to 10.13 = High Sierra, (I don't even know if that's correct....)
or
buy a reconditioned iMac (I really do not need a new computer nor can I afford one).

There's a 21.5" Monterey for £445 on MacFinder whom I have used before, excellent reconditioned Mac seller but the price made me blink; and a 21.5" Monterey for £386 on Mac Store UK, but I've never used them, can't find many reviews of them, and the price difference seems strange.

If it helps, I use this iMac for: web research, emails, numbers spreadsheets, pages letter writing, iTunes and iPhoto. We had to close our business due to my husband's ill health, so my computer demands are relatively light.

Many thanks in advance for all helpful suggestions, as ever.

It is always easy to spend someone else's money, but for a going on 12-year old iMac I would suggest replacement. A sudden power loss seems to indicate something other than "wrong with your operating system". Also, I found the following about 21.5" iMacs:

"… Apple said the 21.5-inch and 27-inch ‌iMac‌ from Late 2013, the Mid 2014 21.5-inch ‌iMac‌, and the Retina 5K 27-inch ‌iMac‌ from late 2014 will be marked as obsolete on November 30, 2022. When marked as an obsolete product, the iMacs will no longer be eligible for any repairs and services."

How about a newer-ish laptop? Also check out Apple's refurbished section in the Apple Store online. They warrant the products as if they are new.