How is the exploration? is it frantic or calm with lost of tongue flicks? Often very stressed snakes will sit and not move at all. and moderately stressed snakes will roam but frantic fast jerky movements. Lazy curiosity is good and a great sign. A snake that always hides is not healthy either. As with most things a balance.
I see no problem with an oil mite treatment it is old school but it does not stress the immune system and cannot harm the snake. To me it sounds like your vet is treading lightly. Treating the enclosure and snake is very logical rather than using toxins that have serious side issues in humans (like P-A-M).
Is the feeding being held down? Is it a powder (critical care -carnivore) that is being used? This also is new ideas it is way easier to digest simple protein and additives than whole prey. Assuming that the balance of stress is managed it seems to be a good solution. Whole prey might bring on a regourge. The baby food for carnivores is easy to digest and gets lots of extra hydration in. It packs a hell of a punch. We have been using it will all sorts of rescues. Tubing a snake should not be done at home getting it wrong is very bad... That is a job for someone qualified.
You really NEED to get the ambient temps up they should be 80 ideally. 73 is very low, low enough to cause a regourge. Core temp is very important and simply warming the belly is not enough is cases of low air temps to raise the core temp. (big lung...) severe hypothermia in humans is treated by warming the blood. Not just the skin.