I may be just stating the obvious, and if so, my apologies. People have different backgrounds and experiences, so it is hard to know when something may be helpful. I am putting this here, rather than a PM, in case anyone else has a little one struggling with sensory issues...
Another possibility, Athene, if you have access to this type of specialist, would be to consult with an occupational therapist with a sensory integration background. This, of course, is secondary to getting any medical evaluations for adrenal, thyroid, etc. The aim is to take a careful look at the sensory profile of the child and devise a set of exercises and activities (sensory diet) that help the child feel less out of kilter with the world, whether due to sensory avoiding or sensory seeking or a mixture of both. There is a look at all the sensory systems (visual, auditory, tactile, proprioceptive, vestibular, etc), and the typical way the child approaches and takes in information from each "channel" I hesitate to call this a treatment, in the sense that it is more likely needed longer term rather than for a few weeks or months, but it can be simple things that fit fairly easily into the child and parent's day.
For instance, for some children, the wearing of tight, spandexy type garments or weighted vests seems to help (as mentioned above). Many benefit from joint compressions (easy to learn) or "heavy work" such as pushing a full cart at the grocery store, or gymnastics class. Many also benefit from skin brushing with a surgical brush (very, very soft). But, there is a specific way to do these so ideally best done via consult with specialist.
The techniques seem to help kids with self-regulation, though good experimental research on this type of technique is sorely lacking... So, if you ask me, "Show me the proof!" I can't. In general, it wouldn't take a child who is so sensitive to textures and turn him into someone who craves scratchy woolens and tolerates tags. But it should help a child get to the point where he will comfortably wear clean stretchy clothes rather than dirty ones! The other thing that eventually does help is maturity, since bright children eventually will wear the clean clothes due to social understanding (even if they are uncomfortable).
http://www.out-of-sync-child.com/ A thorough, parent-friendly book on the topic.
And, if there is an OT, reading this, my apologies also for over simplifying a complicated concept. Take care, J.