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

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

Here's what I use:
Sheet Suspenders

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.

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.

We got one of those non-skid pads meant to place under an area rug and placed it under the mattress. It does 2 things... keeps the mattress from sliding down the slippery wooden platform it sits on, and it also helps hold the fitted sheet in place.

Janss wrote:
Here's what I use:
Sheet Suspenders

Ditto for suspenders

GordonThree wrote:

Janss wrote:
Here's what I use:
Sheet Suspenders

Ditto for suspenders

Use these, also, but got mine at Wally World for about $4/set. I have two sets on the RV King.

We use sheet suspenders as well for our "RV queen" mattress fitted with standard queen sheets. We found the three way style works best for us.

RayTour Bed Sheet Holder Straps

I have found California King sheets fit the best, with no straps or mods.

We have an egg crate pad under the mattress so it doesn’t slip on the pedestal.
Maybe that traps the sheet corners??

There are fitted sheets for thicker mattresses. Might work better.