Diva, thank you for your very detailed "critique" of the Ergo.

It does sound like you're having a very hard time with it. And I agree, it probably just isn't the right carrier for you.

It sounds like a lot of your problems stem from you using the backpack attachment kind thingy. I don't have that, so have no idea how that changes things.
When I travelled to Europe by myself with DD (6 months) I used the Ergo with her on the front and a regular backpack on my back. It worked really well for me. But we're talking older babies here.

I never had any trouble "centering her" or clipping the chest strap together, but I don't have G-Cup boobs, either. Geez, I didn't even know they made G-cups!!!
And I have the chest strap quite high. So it's easy to reach. I find that comfy, but it might not be for different builds.

But one thing I noticed is that your son is only 2 1/2 months old. I never used the Ergo with a kid this young. In fact, don't they usually recommend using the baby insert before 4 months of age? From my experience, babies this young really don't like they're legs spread that far. I used mine with DD from about 3 months, but with her feet tuckd under her, frog style.
You are very right when you say they are more suited for toddlers. I wouldn't even attempt to carry a 2 month old on my back. actually, with a baby this young, I like to see her, so want her on my front.

I hope you like your new carrier better. And, I hope your son will like it, too.
One good thing is that Ergos usually have a decent resale value, so you should not loose too much.

Sasa