Travel tips needed - travelling from cold to hot country. What to wear?

[Witchofzog]

I am travelling soon to a hot country when it is expected to be minus temperatures here. I will be using public transport (2 trains) to and from the airport, and to complicate things I will be travelling to my travelling companions house first in an eu country that is equally as cold. So the plan is
Day 1 - Travel from cold country to cold country
Day 2 - Spend day at travelling companions house
Day 3 - Travel to hot country
Last day - Travel from hot country to travelling companions country and then get connection back to the UK on the same day

The long range forecast says -2 the week I travel so I will need a coat and jumper. But what do I then wear on the plane bearing in mind it will be 35 degrees when we get off?
I need as much luggage space as possible but don't want to be too cold here or too overdressed and hot when we arrive and I want to be comfy on the plane too.

I have never done this before. All my holidays have been in the summer from here when it is relatively warm and I can't seem to get my head around it all. Can anyone please advise me? Thank you

A thick coat etc will keep you warm, a take a wintry outfit for your return too (jeans can be worn more than once to cut down on luggage. Base layers are thin for the warmth they add. A common problem - just don't forget to pack winter clothes in hand luggage to change on the plane!

I normally wear jeans with a long sleeved thinnish top with a thick puffer jacket.
I only take the one long sleeved top and wash it through on arrival to use for the return journey.
As other poster said I change on the plane before arrival. I keep a hand luggage bag with change of clothes, bikini, sun cream etc in case of delayed baggage.

So jeans and a winter top and change on the plane. I always bring spare outfits in my hand luggage so this shouldn't be a problem and I can always wash my winter clothes at my travelling companions home so I don't have to pack more than one set. I think I had it in my head that I needed an outfit to suit both weather's somehow like I do when I go to Europe

Layers are your friend. I regularly do the opposite as I live in a hot country and travel back to the UK or Canada. I'd go with jeans with a plan to change into leggings on the plane, if it's really cold put leggings on under jeans. A thermal vest under a long sleeve top and a big warm cardigan rather than a puffy jacket, maybe a scarf. Cardigan and scarf are more use on a plane when temperatures can be up and down and serve as blankets. If necessary you can wash through the leggings and vest at your friends. On your feet flat shoes or sneakers which may be useful for sightseeing.
Landing in home country (assuming it's not a Muslim one) I'd wear the leggings with a tunic top and change into flip flops.

Thank you @yakari. Leggings and a tunic are my usual go to for Europe as both seem to work in hot and cooler climates. I also have a pair of loose trousers which go well with trainers so I might wear these and then change the top half and shoes when I am about to land.