STYLETHREAD -- LET'S TALK SHOP!

I have a black cashmere hoodie that I love to wear on flights, it's super comfy and not too sloppy.

As far as pants go I love sweats as well and completely understand your dilemma, try a pair of lightweight burshed wool pants, they are wrinkle resistant and look pulled together enough for the long ride.

I think these are the perfect travel pants.

I own a pair and they basically are sweats (and flannel at that!), but don't look like them - they are certainly nice enough for weekend wear.  They can be worn with pretty much any type of slip on shoes: ballet type flats, moccasins,  Puma-esque shoes... so they are pretty versatile.  For tops, I would layer a nice tee (I have and love this one)

under a big comfy cardigan, something that wraps so its easy to put on and take off. 

I like to put really cute slippers in my carry-on (I have some velvet ones with beading)  - I put on foot lotion and those lotion socks to make it a more luxurious flight. 

Have fun on your trip!

I fly Seattle to DC a lot (every month).  I usually wear black cashmere hoodie, with a thin long sleeve tee underneath, so I can take off the hoodie if the flight is too hot, and a pair of black yoga pants from Victoria Secrets or similar like this (but without the stripe):

and I usually end up wearing some colorful sneakers and taking on board my briefcase and huge handbag full of the stuff I need for my flight. 

juicy set in cashmere or velour is key.