If you're looking for MPV-level comfy seat, then obviously avoid buckets.
Semi buckets are still not up to the mpv-comfy level also. If want spongy, then you'd probably have to recushion the existing one.
For me, even the eg6 seats are not soft, but it's a price I pay for driving a lightweight car. A lightweight car can float easily, so I'd rather have a good feel of the road, rather than having a comfy MPV style seat which is comfy, but can't really have a good feel of the road. Kinda depends what kind of comfort level you're looking for. For some, Recaro's are comfy. For me, they are to a reasonable extent, but definitely for people who drive MPV or heavy cars like Bimmers, Mercs, etc, the comfort level is definitely lacking. Personally, I do feel that lightweight cars should never have too comfy (read: soft) seats because they have more tendency to float and/prone to aquaplaning, which makes it important (at least to me) that the driver is able to feel the traction on the road.
Still, if you swing that way, it's your car.
Sometimes, backache is caused by the way you sit on the car seat, so try changing posture first. Usually that is more likely a culprit than uncomfy seats. Sometimes I wonder how people can drive their car when the seat is 90 deg straight up.
For setting seating position, google can probably direct you to a multitude of websites about proper seating position when driving.
