To prevent it from cracking / spreading, you can go to a windshield repair place, I believe many tint shops would do the work. If you are a diy person, you can try a kit like this
I found a great solution. I purchased a seat cushion from Amazon for $19.99. Pulled it from the cover, cut the sides to fit the bottom cushion (minus the bolsters), put back in case and BOOM! Super-Duper comfortable! Also, this is a honey-com gel cushion, so my air condition seats still work perfectly (tested). Long drives here we come!