You will find the best seats in any small car inside a Fiat 500 (the small 500). The squabs are longer than in most cars and can be tilted to support the thighs. The seats themselves are contoured but are relatively flat. Obviously any seats with adjustable lumbar support help. And you should always have the backrest slightly reclined to spread some of your weight into the backrest instead of onto the base of your spine. But the most important factor is a long squab that is adjustable for tilt.