To stop toilet seats slipping sideways, you simply fit Safe-T-Bumpers.
Safe-T-Bumpers are L shaped brackets which you (or someone with a drill and Phillips screwdriver) attach to the bottom of your toilet seat, the arm reaches down and hugs the top of the bowl so your toilet seat is held in place and will no longer slip.
Toilet seat stabilisation also cuts down on the wear and tear to the toilet, helping protect hinges and fittings as well as the seat.
Also most importantly people using the toilet can be happier and more confident as the toilet seat is no longer slipping.
Also good for commode seats.
So how many slipping toilet seats are you making non slip?