Re: Neck/tight trapezius
Structural alignment is important to the overall health of the back. If you can find someone who specializes in bodywork that focuses on the biomechanics of the spine, it would be ideal. Some physio therapists are trained in this sort of treatment.
Good posture begins with a properly aligned foundation. When the feet pronate, it changes the position of the ankle and knee, which in turn often causes one hip to be carried higher than the other, a rotation of the pelvis, etc. which follows on up the spine, often creating imbalances in the way the shoulders are carried, which has an effect on the neck. Perhaps the first thing to do would be to address your overpronation with a properly trained professional (not by buying over-the-counter orthotics!) I think this is a type of alternative medicine that is sometimes called Structural Integration. This seeks to get the body into better balance. "Structural Integrators use a multi-session approach in which specific strategies are developed to guide each individual into optimal balance."
When things are out of balance and alignment, it eventually affects the biomechanics of the spine. Once pain develops, people tend to compensate for the area that is painful...which can lead to more imbalances.
I would suggest you concentrate on strengthening the muscles of the back and core. It is important that one set of muscles is not stronger than another is this causes tendons and ligaments to shorten or lengthen, thus increasing the imbalances.
At work, you should set up your work area to be as ergonomic as possible. You should try to get up once per hour to walk for a couple minutes -- just changing position for a few minutes gives things a chance to rearrange....
and, I would suggest you do the following "exercise" at least once a day, twice if possible (morning and before bed). Lie on the floor or a hard surface on your back, knees bent, feet flat on the floor. Pelvis should be in a neutral position. Place arms as close to the sides as is comfortable with palms facing up to the ceiling. Position head so chin is just barely tipped in the direction of the chest. (The idea is to get as much of the spine in contact with floor as is comfortable and possible.) Now, just relax. Breathe deeply from the belly so the abdomen goes up and down. Try to do this for up to five minutes.
This position allows the discs to unload and opens up the channel that allows the paraspinal nerves to "breathe." It should help with your alignment too.
Since you are used to carrying your head forward this position will feel strange and awkward in the beginning, but you will eventually find it very comfortable and it is so good for all the spinal nerves which affect the health of your entire spine.