Overall I can say NT's are strong offensively, even if they rely mostly on a single action ie no specs or regular hits.
So for a defensive boost suggestion for a prof I feel is unique and handicapped by that same aspect is:
Nano Crystal (Damage Fluctuator)
Attack time 5 sec
Recharge time 2 sec
On use the target will have their damage type changed, after 6 seconds the damage type changes again, and repeats for maybe 5 damage types. Yes it is very similar to the perk effect Chaotic Modulation that is "un"used by agents but this nano affects your target. It would have a 1minute lock on it preventing you from spamming it and the attack and recharge times are short so ou can continue fighting the only way you can
I think a nano like this would be a major boost to NT's against regular hits, which is ridiculous for any prof to die from at tl7, and when soloing. You have no healing, your offense and defensive are locked together so increasing the effectiveness of your absorbs in this manner seems like a great, non OP addition.