I regularly book fully flex domestic flights in Y/J as it gives flexibility to get an earlier or later flight home if needed or to change the date if the meeting date changes. They usually cost around £400 return.

I've also booked long haul Y and W class when I had no choice - i.e. the client mandated Y/WTP only and I did not need to stay over a Saturday night. In those circumstances you can't book into a non refundable fare class even if you wanted to.