Re: Mei tai
The Boba 3G doesn't have an infant insert, but it can be rolled to accommodate an infant. It comes with directions.
The Boba's straps are placed slightly wider on the carrier body, so Usufarmgirl, if the distance between the straps on the Ergo is too narrow, the Boba might work for you. If it's the actual straps aren't wide enough/properly padded for you, I'd look at Olives & Applesauce carriers - the straps are wider and the padding is softer/fluffier.
Barring those, I think a mei tai, particularly one with wrap straps, might be your best bet. There are a lot of makers who convert wraps into mei tais, but you can get a few ready made from wrap manufacturers. In particular, Didymos makes a DidyTai that is SO comfortable. Hoppediz makes a HoppTie that is very similar, but I haven't tried it personally yet. Both have wide wrap straps that you can configure in a lot of ways to distribute the weight well.