first, examine the split between 'more ergonomic' and just 'ergonomic'. in this case, we must preserve the meaning of the original statement: the new design is more ergonomic than the old design. if we change this to just 'ergonomic', we're attaching an implication that the old design simply wasn't ergonomic (and that the new design, by contrast, is) - an unacceptable implication. that gets rid of answer choices c, d, and e right there.

another item to examine is parallelism. in this case, in the construction 'X rather than Y' (or its analogues, 'X and not Y' and 'more X than Y'), items X and Y must be parallel.
choice a: conforming... rather than flaunting... <-- good parallelism!
choice b: to the body's shape and not to flaunting shape <-- logically nonparallel and also awkward
choice c: can't use 'more' together with 'and not to' (these are exclusive constructions, sort of like 'both' and 'as well as': if you use one, then you can't use the other), so we don't need to consider the parallelism in the first place.
choice d: can't use 'more' together with 'rather than'; also, bad parallelism between to the body's shape and shape flaunted...
choice e: more to the shape... than flaunting... <-- nonparallel

in fact, the winning choice (a) is the ONLY choice that properly compares 'conforming' and 'flaunting' in parallel. all of the other constructions also change the meaning of the sentence via their alterations of the words.