I always say "I never used to".

Marianna, it sounds just fine to me too, except that "never" adds a level of absoluteness that is missing in the original negative. In many cases I suspect that the negative would be rephrased as a positive. "I used to not get up until.." ==> "I used to lie in bed until..". I am not sure how much rephrasing to avoid awkward constructions the brain does without us being aware of it, or even if it is possible to find out.

Rod