Never thought I'd be asking this question, but ... Sheets?

I've used these Sheet keepers for years on my full queen mattress. The fitted sheet corners kept pulling loose. I used 3 accross the head of the bed and 1 or 2 down each side. That seemed to do the trick.

I have a "King bed" in our 5er too. It's actually an "Olympic Queen". I couldn't find sheet sets locally and had to order them online.

Here's what I use:
Sheet Suspenders

A standard King size bed is 76x80 and that's probably what the sheets are made to fit. As you can tell from the size of your home King, they are not all made the same.

https://www.tomorrowsleep.com/magazine/king-vs-california-king