For a person with back issues, I'd highly recommend choosing something with two shoulders, not just one. There's been lots of good suggestions on this thread.
The Ergo is nice, but expensive, especially if you buy the infant insert.
I think a wrap is one of the most ergonomic choices. Once you decide to go with a wrap, though, there's like a million choices of which type to use, starting with whether you want it from stretchy knit fabric or firmer woven fabric. Personally, I prefer stretchy knits.
You can easily make your own stretchy wrap from a long piece of knit fabric. Here's a link
to show you how (scroll down just a bit).
If you want ready-made, I think the Moby
is the best. Very affordable, too.
For firm woven wraps, Girasol
, and Didymos
are very popular, but expensive, even secondhand on thebabywearer.com's FSOT board.
Then, there's the Asian-style baby carriers. Mei Tais
, but I think the wrap, with its wider fabric through the shoulders and back would be a better option for you, not to mention that they tend to be a better fit for an older baby.
I second the advice to head over to www.thebabywearer.com
Tons of great info and smart babywearin' mamas over there.