Hi agree there is no right answer - but we need a starting point, and the below works very well for us.
We target 1 keyword per page, however, expand on same for context to the main keyword. So let's say someone makes a blog on "I can't sleep". We would target "cant sleep" - as the head term as in Australia that has circa 1900 searches a month. "Ï cant sleep" is 590 per month. So in this instance, we would recommend the URL for the content www.website.com.au/cant-sleep
The Title
Cant Sleep | Why Cant I Sleep | Forty Winks
H1
I Cant sleep
H2 (Not overly necessary, but if we can squeeze it in)
What do to when you cant sleep
This is a rare term where the grammar is not ideal. But that is what we would recommend consistent with customer queries. One keyword per page gives you a starting point, then as the page is crawled by google webmaster lets you do a deeper dive into what it perceives the page should rank for.
Adjust accordingly and deliver what the customer wants.
Hope that helps.