The saddle is a good place to add suspension, as it carries very little weight penalty or maintenance liability.
I suspect
@raleighnut was not entirely joking when he suggested a sprung Brooks! My Raleigh rod braked 3-speed roadster has a sprung Brooks, and I have actually been using it for riding mild off-tarmac routes recently when the fancy takes me. Before anyone starts laughing at such eccentric behaviour, remember those sort of bikes were the mainstay of rural cycling a hundred years ago where there were still a lot of unmetalled roads, and are still used in the developing world today. They were designed for rough surfaces. It's not unusual for me to go out in the morning on non-work days and do 20-25 miles on a hybrid, tourer or MTB, then get the old roadster out later in the evening before sunset and go and do another 10-15 miles with the benefit of the sprung saddle.