Alright so here goes. I am 5'1" and medium build (darn you baby fat) and my husband is 6'1" and medium build. I will be doing most of the carrying but I would like a one size so hubby can also. We live in a very hot and humid enviroment and my son is a hoss so we need something more sturdy then the k'tan. Don't get me wrong I LOOOOOVE my k'tan but he is just too wiggly and big for it now. Plus i don't have the breeze so it would be too hot this summer. I have been leaning toward the ergo sport but have heard people having issues with baby sitting too low in the back carry position and the only way to fix to issue will give you a muffin top if you don;t have a flat tummy. Suggestions?