They had self inflating mattresses on sale for $29.99. Got me one. Its too long, packed, to fit into pannier or top box, but can strap onto the seat behind me for travel.
Its a full-size sleeping pad, 188cm long x 65cm wide, and inflates to 5cm thick. Glorious!
A much better unit than the last pad I bought, which went down on me deflated within 15 minutes of first use. I was stung $120 for that one, and it was only 3/4 size. Unfortunately, I misplaced the docket sometime between buying it and first use 3 weeks later, and the sports store where I acquired it would not issue an exchange or a refund without the docket.