I really get what you're saying. My "fear" clothes have always been shorts/capris and also anything that emphasized my arms (like sleeveless tops). Thus, jeans/pants+hooded sweatshirt was my goto outfit because I was covered as much as possible.
I basically got over my fear because it's just too freaking hot here to wear pants all the time!
It helps too that for me I lost a lot in my legs (honestly if I stopped losing there today I'd be pretty happy
) so it's taken a big part of the fear away. I still don't wear sleeveless shirts much, not so much out of a fear of them at this point but more that I haven't found any flattering ones yet. Hopefully soon because it's getting really hot here!
Maybe it's a good thing that you have your Christmas party coming up because it will push you out of your comfort zone and help you to try dresses and see that they're not as bad as you thought.
Maybe you'll even start wearing them more often!
Important thing is, though, is to find one that you really love. One that suits your body and you feel comfortable in. Sometimes it takes shopping around a bit but hopefully you find one that works well!