In those situation I use a seat called The Wedge which folds open and has a back so its a lot more comfortable than just a flat pad I have used them before and it kills my back too.
Now I use a Dove style stool but our ground here is mostly flat so that works very well and gets me up off the ground.
Here is the link to the Wedge seat. https://thermaseat.com/product/d-wedge-series-supreme
They have went up in price since I bought mine some years back I think I paid about half as much as they are asking now.
