I upgraded to HTC One to Sense 5.5 yesterday folwing which it started crashing every time I tried to type something. When asked if I wanted to send an error report to HTC clicking on yes led to a further crash. The error reports did not record the cause, because by this stage it was crashing for unspecified reasons. Selecting anything on the screen was enough to do it.
After some investigation it turned out to be the Swiftkey keyboard which was causing it. The app (as it stands at the moment) does not seem to like something in Sense 5.5. I turned off Swiftkey in settings > language & keyboard and this immediately resolved the problem. Now I just need to wait for an update for Swiftkey which will hopefully solve it and let me start using it again.