I have tried a large bolster like that and it was too large for my comfort. I felt crowded, and it pushed me forward enough to make my leg space hard to adjust to. I now have a much smaller, inflatable one that works well for my condition. I over-inflate it, drop it in position, and then let air out until it is just right.
I just looked for it online and found it on Amazon: "Eagle Creek Comfort Lumbar Pillow (Black), but that particular model shows as unavailable.
I usually don't use it in the Boxsters, but most of the time when I fly.
Another thought: During the acute pain times, getting in and out I need support. I have considered installing a grab handle at the top left corner of the A-pillar. For now, I just grab the top of the steering wheel and push up.
Take care.