Hi,
Overall I'm not really against high-collars, its just that they don't really seem like they'd be that comfortable to me, especially for a uniform that is to be worn regularly. For a dress uniform, my preference would be to do without them as well, but I can see why some people might prefer them.
Overall, I guess one of the things that sits in the back of my mind is when on the Star Trek: The Next Generation show a few years in they modified the uniforms to have a high collar it always struck me that the rank insignia might rub against a person's neck.
Early Style ----------------------------------------------------------------------------------------------
Later High-Neck Style
As for undergarments, I don't really have any issues with assuming the Traveller Tech stuff might be much more advanced, though I have my doubts that a one piece type pressure suit would be workable. To me, people (and maybe even other Traveller races) seem to be not really suited to a "one-piece" lifestyle, or to maybe word it better, there just seems to me that there are too many situations where having the ability to remove or pull-up/down either the top or bottom of an undergarment would be desirable.
Similarly, as a person moves about, having a garment in two or more pieces would seem to me to better allow for the materials of the garment(s) to stretch and move to accommodate a person's movements than they would if it were a single one-piece (or even a two piece undergarment where the tops and bottoms are somehow secured together to be able to act as a "p-suit").
To me it would seem that such a garment would likely need to be able to stretch a fair bit to accommodate the bending of a person's knees and elbows etc while not 'bunching" too much on the opposite side of the knee or elbow while also being able to stretch to accommodate muscle flexing and the like. In regular multi-part clothing, as you sit, your lower pants leg can "ride up" just a bit as you bend your knee, and similarly your fore arm can do the same. For a single-piece "p-suit" it's unclear how this might be accommodated.
In addition, certain body parts may require certain special needs, such as the ability to remove seat/moisture and/or provide extra cooling as well as possible added padding or re-enforcement all of which (in addition to the above stuff) makes it hard for me to see a "p-suit' type undergarment as being all that practical.