At various times people ask about support cushions and some people find the standard commercial ones either too big, too small, wrong shape, slippery, not available and so on.
There have been a number of threads about making your own support but these are sometimes not that easy to find.
Here are a number. Please feel free to add to the list.
Uses the leg of an old pair of pants/jeans plus any available material for filling.
Foam or possibly styrofoam with "fleece".
A whole bunch of models in this thread. One with recycled foam, another "bean bag" style, another beanbag style with rice!
Thanks to all the people in the above threads who shared their ideas.