I read this manga a while back, I'm pretty sure it was a oneshot. It was about this mangaka who would take her clothes off while she worked & would use herself as a model for her designs. This guys hires on as her assistant to do the inking, yet keeps getting distracted by her standing around in her underwear.

I have checked all the manga listed with the "mangaka" and "assistant" tags and none match.

I believe you're looking for Mouhitsu Hallucination. There's actually more to it that has yet to be translated.

I think its this one Takidani Koukou Manga Club

Mouhitsu Hallucination is it, thanks.