Greybeard I can confirm a dual seat is no comfier either, what gives me some pain is the white piping around the seat just digs in where it touches you and feels like your sat on a steel rod.
What about a scooter or camping trailer innertube ? they have small wheels and you could inflate the tube a bit then sit on it and when you get where your going let the air out and stuff it in a bag out the way ? Would be a bit like the things they sell for sitting on when folk have bad piles etc only cheaper
