"Sleep tight," one more time

A few weeks ago, I lodged a complaint here about the return of the "sleep tight" etymythology in some media outlets that should know better.  But those were mere bedbug bites compared with what's on the way. According to the Wall Street Journal's review, best-selling author Bill Bryson repeats the legend in his new book,  "At Home." The Journal's paraphrase:

 When parents kiss their children good night and say, "Sleep tight," it's a fair bet that neither party realizes that the phrase originated in the era of straw-stuffed mattresses. Before the invention of spring mattresses in 1865, bedding would have been suspended by rope lattices that, when they sagged, could be tightened with a key.

Bryson, judging by the book excerpts viewable online, doesn't make nearly so big a deal of it; his reference to "sleep tight" is just a parenthesis ("hence the expression 'sleep tight'").  Still, it's too bad to see such a (justly) popular writer spreading misinformation. As my earlier post noted, the phrase "sleep tight" appeared in the 1860s -- just when the new spring mattresses (assuming that date is correct!) should have begun to make it obsolete. "Sleep tight" means "sleep soundly," and there's no evidence it has any connection at all to rope beds.