I agree the stock seat is less than ideal, however I found the so called lower seat, which is a gel seat, is not noticeably lower but for me was way more comfortable. In fact, all day comfortable. I am short of inseam & arm length anyway so the bump in the Guzzi seats really does not limit me. Only caveat, gel seats do hold heat, so on a hot sunny day never park the bike without putting a helmet or something over where you sit. That aside, I have had very good experience with Sargent seats on a couple of my Tonti framed Guzzis, and would use them anytime. As for Corbin, I know a lot more people who swear at them rather than by them.
Try an Alaska butt pad for the seat. The sheep skin should keep the gel from getting hot. http://alaskaleather.com/products/medium-sheepskin-buttpad get a light colored one.