I have a Memaflex seat pad that was meant just for touring but I’ve ended up leaving it in the car full time and because of the slight height increase have the seat lower and further back which gives better legroom too,
bought some black cushion covers cheap off ebay so it doesn’t look too odd. I broke my hip on the right and my foot on the left a few years ago. Can easily do a five hour stint in the car and not walk like John Wayne afterwards.
Memaflex and Permaflex are expensive but the advantage for me of the square pad is it can be turned around or over every time I stop or just moved a bit as I drive to always feel comfortable.