Driver's Seat Cushion Needed. Any Advice?

[Drawingbreath]

Well, I finally took receipt of my second-hand Toyota Avensis TR and have had a decent couple of weeks with it. There was a problem with the brake actuator (which was thankfully fixed under warranty as that would be over £1000 to fix) and the back seat bench is adrift, which is having a new frame fitted to it next Tuesday.

However, apart from the flaky and unfriendly onboard sat-nav my main bug-bear with the car is easily the uncomfortable driver's seat. I suffer from sciatica and the pressure caused by the very firm edge of the seat being so much higher than the recessed area for your backside causes me undue discomfort on the back of my legs. Even though the seats are clearly more luxurious than my 8 year old Micra, I never had such issues with it.

My question is this. Can anybody recommend a thin and effective cushion that works in this model of car without sticking out like a sore thumb or being so massive that is includes needless back or lumbar elements? I was thinking memory foam would be the most effective, but I'm open to opinion.

I hope somebody can shed some light and perhaps some links to an effective product.

Cheers.