Now, this happens to me, as I too am blessed with a cute, small, delicate and perfectly formed nose
I wear sunglasses all the time (well, not all the time, but a lot) and firstly - I can assure you that the 'movement' you describe is not really noticeable to anyone else. It also happens to most people (other than those with roman/jewish type noses) So, I would suggest you just get on with it, its fine, and very normal.
I also, FWIW, have a problem with my eyelashes rubbing against the lenses.. can be annoying, but after ten minutes or so, you forget.
However, if it really bothers you, than I would advise to get sunglesses that have the seperate little plasticy bits that sit on your nose, rather than the actual frame sitting on your nose, as this makes them sit further away.
Personally, I have sunnglasses in both styles, and I prefer the ones without those bits, but you might prefer them.
Hope this helps