I need help too!
I am having similar problems with carrying my 9 month old -- he's also 20 pounds and 28" tall. The one that's actually working the best for me right now is a stretchy wrap kind of like the Kangaroo Korner one. The stretchiness holds him in tighter, even when he wiggles. It's also easy to get in and out of.
The problem with hip or front carriers for me right now, is I can't actually do anything while using them except walk around (helpful when we're out of the house!) His reach is as good as mine. This morning he dumped my measuring cup of veg oil, molasses, and maple syrup (making granola!) on the floor while I was wearing him. But if I wasn't wearing him, he'd be squealing and carrying on and I couldn't make my granola anyway.
I have been experimenting with back carries (although I don't have a variety of carriers to try) without much success. My problem with the ones that tie, is that I am having issues with my left wrist (seeing a chiro) and there is no way I can pull it tight enough that he is in the wrap securely. I had a front-to-back backpack style, but it is a huge pain to get in and out of, and is absolutely useless when I am home by myself (all but a few hours every day!) I like the idea of the woven wrap carrying him high, as I'm sure this would be what he's most happy with at the moment. Just not sure I can do it with my wrist. (I have a woven wrap that is pretty lightweight, wasn't originally intended for babywearing, it's kind of stretchy which seems to be a problem with his weight, even though the other stretchy one is great!) Are there any other styles that would do a back carry easily with one person?
I went to a thing the other day with other moms who were all carrying their 15 - 18 month old babies in the front with bjorns or mei tais. Their babies seemed to just hang out there -- no twisting to grab this or that, trying to dive here or there, just went along observing whatever mom was doing. It made me wonder whether baby wearing, while very helpful for a very "active" child who wants to be held, is also just simply more difficult! Is this a fair assessment, or is there something I am missing?