I have chronic back issues including sciatica To explain a bit so you can see if you have the same problem, I am uncomfortable in anything that presses against the side of my leg. Examples are the folding chairs that fold up like an umbrella, soft chairs and couches, and any car seat with bolsters. Here is my fix.
I found some very stiff foam rubber. 1 7/8 thick. this stuff is so stiff or firm that if you kneel on it on one knee your knee will not bottom out. It is stiff enough that I cut it with a circular saw.
I believe it is the foam from M 151 Jeep cushions.
I made a cardboard pattern of the Mazda seat cushion inside the bolsters. Then I made a cardboard pattern of the width and angle of the bolsters at the back and at the front of the seat.
I cut the foam to just fit. Basically I filled in the space between the bolsters so I have a flat surface not a bucket.
In the wrong car I can drive for 30 min to a hour. In the Mazda with this cushion I am good for 10 or 12 hours with a couple of 5 min stops.
"The trouble with bucket seats is not everyone has the same size bucket."
