Who doesn't have back problems amongst the Baby Boomers? If you don't, well, you probably will eventually. Call it the ravages of time. Never mind younger folks with injuries or other medical conditions.
If you're thin enough you can continue to carry IWB but you have to remember that any IWB carry, even small automatics*, puts direct pressure on muscles, hips, etc. That's why I recommend OWB for concealed carry if you're going to go with a belt holster. OWB puts weight on your waist and hips but not direct pressure and if the gun is lightweight it's usually not as big a deal. So if you're going to carry a belt gun I recommend OWB. Many IWB holsters are comfortable but the direct pressure is still there.
*The CS-45 doesn't qualify as small in my book - concealable, yes, but it's not small. I love mine but I avoid IWB carry these days.
That said, I go with the guys above who recommend pocket carry. Carry a lightweight pocket pistol or Airweight S&W or similar wheelgun in a well constructed pocket holster and your back won't know it's there. When you're standing/walking, etc, the gun is just some small amount of additional weight supported by your trouser belt and of little consequence. When you're seated your back doesn't have a clue that there's a gun in your pocket - there's no weight and no direct pressure. It's ideal.
THE SOLE DRAWBACK to pocket carry is the inability to do a rapid draw from a seated position. But in a vehicle you can either have another weapon accessible or remove yours from your pocket (discreetly, of course) and make it available to yourself.
I recommend pocket carry very highly and nobody will even know you're doing it as long as you're carrying a small, lightweight firearm..
