Try blocking in the entire body, rather than concentrating on one area and detailing it. You'll be able to get a feel for what is proportionally sound that way. I think the reason it looks weird when you followed Helm's guidelines was because you stretched out the abdomen without thinking about the structure (from what it appears, anyway). Biggest things I notice with it are that the abs are basically floating up away from the lower belly and the torso isn't built around a ribcage. Maybe your focus on the breasts as a silhouette is misconstruing your construction of the figure itself. Try imagining just the torso with no breasts at all, and imagine the shape of the volume, the roundness of it, and the planes, and see how the breasts occlude the ribcage, rather than replacing them. Crotch also seems too high in Helm-structure-reform you've done.
In regards to various parts of the body varying in size, etc, that's true, but there's still the issue of the body being in proportion to itself, which can't really be gauged well at this point with the figure being incomplete.
So basically: concentrate on whole form, come to detail when the whole is realised.
