I tend to wear v neck t shirts alot. Long sleeve in winter, short sleeves any other time. link like this only my boobs are much bigger than the models- they're D cups. You can see a little bit of cleavage, but not too much.
I know exactly where you're coming from since I have D cups too (creepy first sentence much lol).
I have a few shirts like that myself so needless to say, I don't think that shirt is ugly; I think it's casual, comfortable, and flattering for girls whether they have A cups or E cups. Overall, it's just a classic that you can never go wrong with. The whole "t-shirt and jeans" kind of gal that people always mention, well, that's her shirt! haha.
And if you want to dress up on a different day, then dress up on a different day with a more fancy shirt or sweater. Or, you could also just accessorize a bit more and look just as good! (Think like a nice necklace, or maybe some funky dangly earrings, etc. Or even a comfy fitted cardigan over top of the v-neck t-shirt.)
I think it's fine! Wear whatever makes you feel comfortable, that's my philosophy!
It's okay since it's not a deep V
I have big boobs and I find that scoop neck, crew neck, look better because the roundness of the neckline complement the curves and it looks a lot more classy. I also think turtle necks have the same effect. Vneck, boatneck, and off the shoulder are more flattering for girls with smaller chests, especially a deep v-neck or plunging neckline.