One thing to be aware of with the full buckle carriers, is that you need to be flexible enough to do up the strap clip at the top of your back (i.e. near your shoulder blades). I just couldn't reach the straps well enough to do them up. I'm not horribly inflexible, just didn't seem to work for me. So I think you need to try it on in person before buying one.

I have a mei tai that I bought 2nd hand on ebay.