I decided to take the Z125 for a long road trip the other day and after 30 minutes, things got really sore (ended up riding for 4 hours straight, ouch). $363 is a steep price, but it's a must for long distance travelers.
I have a Corbin seat for my other bike (2008 Kawasaki Versys) and can vouch that they're going to be much more comfortable than the stock seat. Unfortunately, they're not as aesthetically pleasing but they at least give you options to customize the looks to a degree, as wvabeer stated.