Revised 21 June 2019
Sorry if you’ve come here because of the title; I’ve had to delete most of what I’d written because it’s no longer correct. It was based on using a site (Online Sitemap Generator) where you can make a large sitemap.xml for free (though you are encouraged to make a small donation). I’d used it for about a year on and off and was reasonably happy with it, although I did need to edit the files quite extensively, which was the point of the post.
Things have now changed at this site; I get a lot of errors when I try to make a sitemap. The resulting file is unreliable so I’m no longer using the site.
I haven’t been able to find another site which offers free sitemaps for more than 500 entries. My book reviews page has almost 600 reviews so that’s no good to me. I’d be willing to pay a reasonable amount occasionally but the charges I’ve found on-line are more than I’m willing to pay on a recurring basis considering I don’t get any income from my reviews.
For the moment my solution for the book reviews page is to keep the last good sitemap I obtained and add new entries by hand. This isn’t a problem as I don’t often write more than one review a week at most.
For WordPress I’ve installed a plugin which provides a sophisticated sitemap.xml system which seems to be working well (google-sitemap-generator.4.1.0).