You could get one of those super slim cases for your phone. While they don't offer a whole lot of protection, it should be enough to at least keep your phone from getting scratched up without adding too much bulk.
I used the bumper, and now have a hell-load of scratches on the bezel where dust and crap has got between the bumper and the phone :'( I think this might because it was one from an early release of bumpers with softer rubberised buts, as ones that I have handled since have a much stiffer rubber on them (and have not let in any dust).
Use an invisible shield for the front and back though. They take a few minutes to install, but have a nice feel to them and protect against any scratches
I have just a case on my phone. No screen protector.. Honestly I don't understand why people become so overprotective of their device. Why would you protect something to resell later? You don't even get the real joy out of using the device. It's like you're saving it for the next person to use. The only reason why I have a case is because I drop the phone a lot. Or I'd go naked without it. Use the phone the way YOU want to use it. You're going to get a new phone in a year or two, so you might as well enjoy the amazingness and slimness of the phone.
I have front and back protectors, i am ocd-ish but honestly you cant even tell they are on, so it protection without any notice. I did also throw on a bumper just for the minimal "lay on the table" protection.
I forgot to mention with my sgp protectors it also included side protection which i did put on and have the bumper over it just fine. I guess i am more ocd then i thought.
I use an Incipio Feather case and love it. The front glass is bare. I keep the phone in a pocket by itself, and I don't put it on tables face-down. I know, it's difficult.
You get a much better experience using the iphone naked, especially the screen. No screen protector can compete with the naked glass. Personally I use a leather pouch for protection in my pocket but the iphone is naked in use. I've tried a bumper and screen protectors but felt wrapping it in plastic spoilt it!