We always encourage communication for them, and to speak about future plans...keeps the mind forward thinking and helps them not to ruminate.
Perhaps you could ask him if he wants some photos sent in of his cars, family etc. Some families will send magazines in for them (maybe car modification ones etc)....gets the mind thinking etc
Not having a CCO isn't necessarily a bad thing, most prisoners do not want them as it sets them up for failure if they breach it. Most would rather do the extra time so that they can be released with nothing hanging over their heads....straight release it's called.
Jail effects everyone different, large crowds and shops might not bother him...I'm sure you'll be able to read his body language or tell if hes avoiding certain places/situations.
PTSD is quite debilitating, it's something I struggle greatly with....it's physical as much as it is mental and when those triggers occur it is very hard to rationalise what is happening in the moment....which is why he turns to drugs....it's a coping mechanism but not a healthy one.
I find when I am at my healthiest I am maintaining a good routine, no alcohol, exercise, work, hobbies etc. When something breaks that chain of routine the train comes off the rails very quickly and alot of damage can be done in that short window while you correct yourself.
Personally I have not found psychologists to be helpful/make any difference, that's not to say they do not help or have effective techniques, just that for me personally they have made no difference, and on occasions I feel my health deteriorates when seeing them.
Everyone is different, but I feel the key is knowing your triggers, knowing the root cause of those triggers (where in the past do they come from), acknowledging those triggers and accepting they have occurred but do not control you and cannot hurt you now.
PTSD is such a complex illness and there is no one solution for an individual, its a blending of multiple therapies, medications and life experience for what works for you.