Chris I know exactly what you mean mate, my back has been terrible for years, from way before carpet cleaning, and I'm only 34!!! As already suggested try spending £100 on a glide first rather than £500 on a new wand
I wouldn't be cleaning carpets any more if I hadn't started using glides quite a few years ago. You'll wonder why it took you so long
There's absolutely no way on earth a glide fitted properly can leave a carpet wetter
You might get on with a light wand but they do still present their own problems - on some carpets you have to push them down into the carpet to get a vac seal, which still gives you back ache. They will also 'chatter' across a polyprop pile if it's matted down a bit.
I've tried one of those evolution wands and thought it was an absolute bag of s**t, worse even than a normal stainless wand with NO glide.
You might also do well to really analyse your wand technique - I'd like to bet you're stooping and/or over-stretching! Your posture should remain upright, never stooping, and your length of wand stroke not too long, just the limits of the reach of your arms. Yes it's quicker to extract with much longer strokes but also a quicker way of crippling yourself.
Do you lift the wand up off the carpet between strokes? The weight of a wand shouldn't matter if you keep the wand in contact with the carpet and use push & pull strokes, occasionally twisting it to let a rush of air up to clear the hose out. You'll find a glide makes that technique a doddle.
You should find with a glide you can use longer strokes though, as it is so much easier to operate the wand you can do it one handed between thumb and forefinger on a lot of carpets