I recently replaced a toilet seat in my house.

But the new one tends to slip a lot - VERY awkward to be sitting on a
slipping and shifting seat, obviously.

I'm pretty strong and have hand-tightened the bolts as much as I think
is reasonable, and the bottom line is that, subjected to the forces of
use, this seat continues to slide.

So I'm wondering if they make rubber washers or gaskets that fit between
the actual toilet fixture and the plastic parts that hold the bolts -
just something to take friction out of the equation.

And if not that, short of tightening the bolts more (they're as
hand-tight as I can get them) or getting a new toilet seat (seems
excessive), what else could be done to prevent the seat from slipping?