Mmmmh, as you can se below, I'm not nearly as far in as you, and I'm still quite more hairy than that. However, it did begin to reduce. The visual changes aside, what I noticed the most was the growth speed. My hair regenerates really slowly compared to before. I went to the laser clinic last week for an evaluation, and I was told that they weren't able to determine if my upper arms were treatable, because waxing was too recent. But guess what -- that was one or two weeks before Easter.
Also, whilst before, shaving my torso would see hard stubble just 12 hours later, now, over one day after the shave, it's still relatively smooth and very subtle.
My point being, waxing is probably going to be very effective. If your hair has slowed enough it should last for a while. And if I remember well, you have an epilator and are able to endure the pain even on the torso, yes? If so, it should be easy to maintain the waxing's results by quickly passing the epilator to remove the little gradual growth often. You could even make a habit to make it a minor, 15-minute task every night, so it never becomes a pain with a ton of hair. And, well, regrowth from waxing tends to be quite fine in the beginning, I think, since it's the pointy tip of the hair that comes out, so that's a plus too.
Also, depilatory creams are... well, all right. But be careful. Basically, they dissolve your hairs that are outside the surface of your skin, and a little bit under it, too. In a way, it's like a super shave, in that the hair is still there and healthy, but it's been "cut". So you'll have a full-thickness hair growing, just like with shaving. But unlike shaving, the hair starts a little bit under your skin, and doesn't have its pointy shape since it's been cut off, so it might have trouble coming out... That's how I understand it, anyway. Because for me, they're an express ticket for a ton of ingrown hairs. So if you're prone to them like me, be careful. (By the way, I don't -know- that's how depilatory creams work... I just deduced that from the speed of regrowth and the number of ingrowns. I might wrong.)
There's an alternate option, too. If I understand well, some of your hair is very fine, similar to vellus, except it's dark? Would you like to try bleaching it? Maybe it'll be just like vellus then and you won't need to worry about it much.
But before trying all that, are you -sure- it's not suitable for laser at all? Because my understanding is that no matter how fine, dark hair works. If it's not dark enough, you could look into dying it. I don't know much about this, but I read a story of someone who managed to get blond hair lasered by dying it black before each treatment.
As for your back, I don't see any other way than getting it waxed by someone else, be it a friend or relative you're really close to and who doesn't mind or a professional at a salon. It shouldn't be too expensive. Or well, if you really wanted to do it alone, you could spread depilatory cream on a wall, and rub your back against it... but meh.
