I know a woman who has a D chest and wears turtlenecks very well; in fact, she lives in them in the colder months. I think the key with her is that she has a super long neck, very strong shoulder line, and teeny tiny waist. And (I suspect, but don't know for sure) fake breasts. Actually, she is kinda built like a barbie doll... so I guess what I am saying is that you just don't know unless you try.
Meanwhile I look absolutely horrid in the vast majority turtlenecks. My neck is so short, I literally look like a turtle...
But, I wear them anyway when it's frigid cold here in Boston, and I have found some that work okay...
Ana, *all* my t-necks are from Jcrew!!! About 5 years ago I invested and stocked up. So I have the wool cable knit t-neck in pink, grey, and a stunning blue and green color. I think these work passably okay on me because:
1) The t-neck isn't too long.
2) The fit is form-fitting, not overly loose, which on me draws attention to my strong shoulder line, and not so much the neck or breasts.
It's still not my best look, but they are definetly cozy and very well made sweaters in pretty colors.
Hmm, I think I have a photo I could post, so you can see how they look on me... hold on a sec, be right back!