What I would do is get rid of trap sense, uncanny dodge/improved uncanny dodge, and the standard DR. Have them gain natural attacks when they shift and make all the natural attacks primary. As for losing the ability to use weapons, just make them only proficient with simple weapons and natural attacks or possibly a very limited list of weapons such as the druids list or the wizards. As they level make the natural attacks deal more damage, count as magical at a certain level (like a Monks unarmed strike), etc.
If you want to make their natural attacks even more appealing make the equivalent of rage powers and let the natural attacks take on properties similar to weapons such as corrosive or icy. Maybe even make the shift a little more like an eidolon so that no one is the same when they shift. Give them a pool of evolution points to spend in various things. And then let them shift into a four armed beast of some kind with a bunch of claws. Or perhaps a snapping turtle man with a bite and a swallow whole ability.