I don’t fly, but have taken several long (llloooonnngggg) train trips, on which I “sleep” in my clothes. I don’t aspire to looking extra fashionable, but I do like to be a bit polished, matching and appropriate. My outfit of choice in warm weather is elastic waist (cropped length, woven, yoga/sport) pants, short sleeved knit top, light weight, coordinating, zippered knit jacket or hoodie, and Converse tennis shoes. I have a small fleece blanket in my carry on bag. In cold weather, it’s basically the same, but longer pants, long sleeve shirt, add a scarf, and booties instead of tennies.
The slacks are lovely and would be a great choice IMO if they are not fussy to manage with your other garments. A colorful knit top, silk scarf, soft cardigan and sophisticated travel handbag would be good accompaniments. A floaty cardigan is a nice idea for cuddly comfort but if it’s very long, would annoy me and get in my way when changing positions in my seat, keeping it out of the way when going to the restroom, and getting my things up and down from the overhead rack. I would not choose sandals - don’t want to sound freaky, but articles on travel safety long ago convinced me to always wear close toed, fairly sturdy shoes as a “survival need” when traveling by air or train (in case of accidents.) This also would preclude any options of tank tops, shorts, or sundresses for me.