I'm with Southpaw... I haven't seen a new truck with vinyl seats in years. My 2008 F250 has cloth seats, and after 7 years and 70,000 miles they still look great. This isn't the "velour" fuzzy type cloth, but surprisingly heavy duty material that really holds up.
If you do get vinyl, I really don't think you'll have any issues with longevity or cracking. By the time the seats start looking bad, the rest of the truck will be showing its' age.
Normally I really don't like seat covers, but a friend of mine who has yellow labs got seat covers for his Chevy 2500. He looked around a bit before buying, and got high quality covers that don't seem to bunch up and slide around. I don't know what brand he got, but they seem to work great. He also carefully followed directions on installing them.
Also, as to option packages, definitely get the "towing package". Usually it comes with pre-wired trailer plug at the bumper, a factory hitch installed, larger tow mirrors (heated and power sliding mirrors may seem like an unnecessary option, but they are really nice to have!), larger cooling for the engine and transmission, a built in brake controller, maybe a few other things. The tow package option is worth it!
Don't automatically assume you won't be getting a higher optioned truck. Many times the "option packages" that are offered make the fancy trucks hardly more expensive than the stripped down trucks. You'll also find that a lot of the options end up being darn nice to have after awhile.
I just noticed you are thinking of a crewcab with an 8 foot bed... you do realize those are about as long as the Titanic, right? My crewcab "shortbed" F250 is pretty long, and I have found the bed to work just fine for the large majority of what I need it for.
Have fun looking, and good luck dealing with the car salesmen!