Agree with everything here, but am surprised the one single thing that gives the biggest increase in comfort hasn't been mentioned.
-
A good sheepskin seat cover.

I first fashioned mine from an old but good-quality sheepskin coat back in 1996 for a trip to Ukraine and Russia. Never did I find a better device for greater comfort.

That old coat provided a few covers for different bikes and I just used the last piece of it to renew the cover on my Yamaha.

So I looked on ebay to see what's for sale.
You can find old coats selling for 30GBPounds or less and in my opinion, the old ones will be far better quality than the newer.
(My coat was originally bought second-hand by my Dad in the 1970s, so age is unknown. Probably 50s from the style of it. He gave it to me and I wore it for many years until 'wear and tear around the edges' led me to find this new use for it).

__________________
TTR250 - London to Cape Town

couldnt agree more lambland uk offer sheepskin covers i think i paid 12 quid for mine it makes a huge difference and provides a nice bit of added comfort for my feet when using my 3/4 rest mat.

I'm aware of the comfort enhancers although none that I've tried offer a vast improvement. The best bike I've ever ridden for comfort was my MG Spada Royale which had a very good seat and an effective fairing. I suspect reducing the wind pressure on the rider as well as all other ergonomic factors affects the comfort of the seat. BMW used to say that their RS riding position (leaning slightly forward) was best but I always found the RT (bolt upright) was better. It seems to me that more recent bikes are worse than their predecessors with their seats designed to suit the styling sometimes detracting from their effectiveness. I used to think that the seat being wide at the front and supporting the riders inner thighs was the answer but then the 1150GS had a very wide seat at the front whilst managing to be the most uncomfortable bike I've ever owned.

Apart from converting a bike into a 2 wheeled car (as per a Goldwing) where the rider sits in still air on a seat that is bigger than most cars, there doesn't seem to be a formula that works for riders of all shapes and sizes. With the technology that now goes into virtually every other aspect of bike design I would have thought manufacturers would be trying harder to solving one of the main limitations of motorcycle design.

Not the topic, but I feel that strong wind may be more tiring and won't allow you very long rides, but I find it healthier for your back: you are forced to pull with your arms and push forward with your back to keep you there. Your neck must stand that force as well. It feels you work out your muscles, including the ones alongside your spine.

By contrast, a high windshield, where you are on still air feels like sitting on a stool for long hours: it may allow you longer distances and more confort, but I wonder if it is any better for your back. Unless you have a good back rest behind you.

It sure varies from person to person, back condition and the like, but I wonder anyone feels it somehow that way.

PS: Look at the huge/wide saddle on a beautiful Honda CB900 Bol d'Or, it does not look stylish for today patterns, at most you could accept it as retro, but people do not seem to love riding sitting on armchairs.