Medium cruiser is the correct size as everyone mentioned... But get the new and improved air hawk R model. I spoke with the designer the other day. It has Redesigned cells, and a wider gap between the main cells, eliminating hot spots and pressure points on the anus, prostrate, and scrotum.
Just google air hawk R.. They retail around $199 but you can find them cheaper on amazon, or eBay
Spanky, if you see this, post up on how you like your R model.....
JJ