I am trying to build a nice professional wardrobe, and in the process, looking to find a couple of nicely tailored sheath dresses. I am having all sorts of troubles fitting them and my most recent failed attempt is a great illustration of all the issues, so I am posting it here hoping for some possible solutions.

The dress is in question is a beautiful aqua sheath by Black Halo. It arrived yesterday, and it was the last one, so I do not have an option to try it in any other sizes. The material is beautiful and thick, very structured and only a tiny bit stretchy. The dress is in my usual size 2, and fits well on the hips, and does not fit at all in two crucial areas:
1) Waist - it is too big. I have had this issue for as long as I remember, and see no trouble at all in having an item taken in at the waist as long as it fits well everywhere else. A second part of the waist fit issue is that I have a very long torso and narrowest parts of dresses often hit me above my narrowest point. Sometimes that works to my advantage as it visually shortens my torso, and with small alteration the dress fits well. More often then not the dress looks all sorts of wrong so I just walk away from it. Here, I think it is the first case, so the waist alteration would solve the issue. (I am holding excess material in some of the photos)
2) Chest/armholes: too tight. I can not lift my arms comfortably and the material feels stretched to the limit. This is relatively new fit issue for me and has me a little perplexed. My body type is hourglass, but it is my shoulders that balance my hips, my chest is smaller. Moreover, I have gained about half a size a year ago and most of that weight has gone into my hips, so I really don't get why I would need a bigger size on the top than on the bottom.

So, while there doesn't appear to be much I can do about this dress (correct me if I am wrong), I am curious how to deal with this in the future when looking for sheath dresses, especially sleeved.
1) Possible alterations - question for seamstresses: how involved/doable would an alteration be if I got a sheath dress that fit my upper body? Presumably it would be two sizes too big in the waist and one size too big in the hips. The dresses in question would have lots of tailoring, darts etc.
2) Is anyone aware of a brand whose dresses would fit a body type like mine: long torso, narrow waist, wide-ish shoulders?

Any other input on this issue is more than welcome!