I am in the market for a way to comfortably carry DS on my back (he is 8 months, 17.5 lbs). I am thinking about either a Bamberoo MT or an Ergo. I have trouble with my sacroiliac joint due to some pelvic instability and need to find something that won't aggravate it. Also, I don't much cushioning at 109lbs and almost 5'7". Which brand of carrier would you recommend and why?