It’s been mentioned a few times. But providing you can get past the looks the BMW 1 Series really is a strong contender. Comfort, economy and great handling. Improved if you run normal tires rather than run flats.
All BMW diesels are very comfy- but do come with a certain image.
According to a number of car magazines, the most comfortable recent cruiser was the pre-facelife Passat CC. I haven’t driven one so can’t say.
Mercs are super comfy on motorway, but clumsy around town.
Volvo’s are bad on fuel but very comfy seats
Saabs- yes they are Vectra’s but super cheap and very comfortable seats.
Worth looking at a car with a good quality sound system as this does make a difference. My last A6 had a relatively basic stereo and the tiny noise did wear me down.
I find Fords and cars from the Far East very tiring on motorways, they don’t seem to settle at motorway speeds like European cars do.