I have a friend who swears by her Ergo carrier. I have looked at them and am jealous I didn't get one when John was younger/smaller. It doesn't have a frame, but it is a backpack type carrier. She says it is more comfortable than the Mai-tei for both of them, and can convert easily between her and her DH. I don't remember the website for it, but you could Goggle Ergo baby and find it.
I have an Ergo Baby Carrier, which my mom got me after she saw a woman wearing her baby in it. I was skeptical at first, I was already happy with the Baby Bjorn I was using at the time. I didn't like it at first, but I tihnk it was more because of my baby's size at the time, it was hard to get her into it and she did not "help". She was fitting better in the Baby Bjorn back then.
But I LOVE the Ergo Baby Carrier now!!! She's 13 months now, more than 17 lbs, and she fits into it much better than when I first got it. And she loves getting into the Ergo Baby Carrier (big smiles!), she thinks it is much better than being strapped into the stroller (which she hates!). The Ergo Baby Carrier is comfortable, I can wear her a long time with no discomfort. I hardly notice her weight, except when she decides to lean too far over to one side (who knows what is going on in her mind when she is suddenly interested in looking at something on the ground, lol). DH also likes using it too, and it is never difficult to adjust the straps between the two of us (he's 5'6" and I'm 5'). I like the sleeping hood, it took me some practice to get it on her, but it's nice to give her come cover if she happens to fall asleep, and I think it helps prevent her head from bobbing all over the place.
Here's the website for the Ergo Baby Carrier:
http://www.ergobabycarrier.com/