The reason you can't find carriers that forward face for heavier babes is that it gets really difficult for the wearer to support that much weight in that position. Having the babe face you is much more ergonomic for both of you. I'll echo the pp and suggest trying out hip and back carries with your Ergo.
Search youtube for instructions on different ways to get the babe on your back for the back carry. My favorite is the superman toss (not nearly as scary as it sounds) there's also the hip scoot.
ETA some videos for you
hip scoot another
hip scoot, slightly different w/ how to get down.
I couldn't find a good video of superman tossing w/ an ergo.
This is a MT video, but she superman tosses.
ETAx2
This one is even better. 5 different ways to get baby on your back and good sound.