I had a very similar problem with DS--21lbs at 6 mos., super-tall, very, very solid, and very particular about everything, especially how he likes to be carried!He loves to face outward and look at the world, so the mei tai didn't work, and he does not (yet) like to be carried on my back, so the Ergo didn't work for us either. I got an Ellaroo Mei Hip and I love it. It allows me to do a hip carry with extra support and he's happy, comfortable and can look around.The other thing that worked for us as a last resort was to bring the infant car seat/carrier along to the store (he hasn't fit in it for use as a car seat since he was 7 weeks old!) and snap it into the front of the cart's seat area. We prefer to carry him, though. Good luck!