Purchase a larger motorcycle quick!

 

While you're getting your seat thing worked out you should look at shocks, like you said.
If I remember from when I had Progressives, any combined weight over 250 lbs. required their heavy duty springs. Not until I got Ohlins shocks did I find real comfort. I'm sure you would, too. They get set up for your weight and what kind of riding you do.

 

Mustang Wide seat will be a huge help. The wider the seat the better it will spread your weight. 10-12 inch baby apes will be very comfortable yet low enough for a guy of your size that your hands/arms won't go to sleep after an hour or so. Throttle boss or rocker to help your wists. Better shocks help with ride quality for sure. Windshields are fantastic on long hauls too, both for the obvious wind busting reasons but also as weather protection.

 

Contact Mean City Cycles about your seat. He may be able to modify your factory seat to your liking.

 

Any shocks gotta be better than the stockers. Progressives are going on mine asap. If you can throw down the coin for a Corbin, do it. I'm personally not a huge Mustang fan, and after a 3000 mi trip, no sore *** at all. 600+ mile days too. Windscreen woulda helped, but I hate the damn things. PDX to Reno is only 9 hrs or saddle time, max, so not too bad

 

Go with the Mustang Wide, invest in a wind shield ( big one ) or a detachable fairing

 

Mustang Wide:

 

wtf cycle shorts on a harley maybe this guy thought he was riding a 10 speed bike.