I wear jeans a lot, here at home in winter, in summer and I definitely take them on trips to Europe. Have never found a problem with being too heavy, too wet, too whatever. Have got lighter weight ones in summer and a bit heavier in winter.
The climate where I live is wet and cold in winter - never have an underlayer beneath any kind of trousers except if I am actually going skiing or hiking.

Bingo!

I agree that a coat for the cold is going to be more important than a coat for the rain. I've never seen silk thermals in Australia. Thermals are available but different fabric - usually man-made something or other. Uniqlo might be good but doubt they'd be silk. Buying silk thermals for one trip seems a shame, maybe try warm tights underneath trousers instead?

Kay

FWIW, silk long johns, etc., come in at least two variants AFAIK. One variant is a true thermal, by which I mean it is a special knit designed for trapping heat; they appear to have a bit of a textured pattern. The other is simply a flat knit. I have generally used the flat knits.

melnq8 is right - it's a lot to do with our own personal thermostat. Just as I am sometimes bemused by some people's preoccupation with the need for airconditioning in summer, when you're like us and live where a winter's day has a maximum of around 15C, it's easy to be concerned about being cold (and I live in the south of Australia - Queenslanders have a different thermostat again!). We like to be outside as much as possible and don't want to be unable to do certain activities because we packed the wrong clothes.

I've been surprised by the level of interest in my query - but have also garnered lots of useful ideas and opinions, which is what this forum is all about and I'm very appreciative.

I figure it's going to be cold every day and only rain some days, so will opt to take the warmer coat - and if there is room in my bag, I'll pack the other one as well (but suspect there won't be). I'll also be packing some long johns but what kind I'll have to decide. As Kay rightly says, silk ones seem to not be readily available in Australia but I could buy from overseas.

In my opinion the silk 1st layer do not keep me warm. I instead use leggings or warm tights. I need something with cotton for warmth. The area from my knee to my thigh oddly enough is what gets cold. Last year, I bought jeans that are warm inside and I like them. I've never had a problem with getting wet except for Iceland and my recent trip to Ireland. I mostly take jeans and corduroys but I am just walking around and sightseeing. I don't hike. That is my style and what I feel comfortable in.

Saying you lived in Australia, is like saying you lived in the US. Northern Queensland is very different to Tasmania, like Seattle an Florida maybe?

Please report back to tell us what worked for you. Have a great trip!

All I can tell you is that we were caught unprepared in Salerno, Italy, in January 2017. It snowed. We froze. If the longer, waterproof jacket will allow a warm sweater underneath, and if you pack a hat, warm gloves and warm shoes/boots, I think you will be okay. On the other hand, you admit to being used to warmer temps and I myself like the cold. I totally appreciate the concern about space in luggage.

I recently bought a long vest (wish I had had it in Salerno) which easily fits under every coat I own. It makes a great lightweight jacket with or without a sweater. With a sweater and under a coat I keep very snug. The vest actually packs down into its on pocket. Takes up no room at all and you can stuff it in a carrier bag just to have on hand. I bought it online from Land's End and I doubt it was expensive.

Except that in Australia it's h-o-t and h-o-t-t-e-r.

Dreamon--I laughed so hard when I read "I've been surprised by the level of interest in my query"

I have to admit...I've been hesitant to contribute to a lot of posts now, even in locations I know, because my knowledge has become outdated, but when it comes to "my layers", I'm an obstinate cuss, especially since I've been living for months in two different climates:

• One varies between 25 degrees F and 102 degrees F.
• The other varies between 10 BELOW F and 95 degrees F.

Layers are my life. And since I live in two different apartments, clothing must be super practical and super limited.

Packing lists abound on my computer for temp variations; hence my detailed contributions to this specific thread.

FYI, as a female of a certain age, I only truly thrive now in a 68-degree or below temp. Yes, my husband wears layers to bed because I have the AC down to FREEZING.

So when I say I wear silk underwear in Paris with such a high personal thermostat, there are reasons:
a) I need to keep out cold/wind when it's really cold and
b) I need to keep cool when I go inside. The thin second-skin type silk underwear does the trick.

I love my fleece stuff, still. I have both a heavy fleece jacket and a light fleece jacket I wear everywhere between the two different apartments, because when they get wet, it's not a problem.

And I forgot to contribute the key thing to the jeans discussion--
ONCE DENIM GETS WET IT DOES NOT DRY. Even apartment rentals in Paris don't have great drying facilities.

Just toss this post when you need to toss it. Again, YOU get to go to Paris this year; I have to stay home to help my oldest daughter and her family move to a house (thus meaning they won't travel!). ARGGGH.

Trip Envy Be Me,
AZ

If it's a short length, you freeze your bum off anyhow. Always cover to just above the knee if you want to stay warm.

also wear a hat and gloves.

Nah

The North Face. Because it's knee-length

London is usually nowhere near as cold as Austria and Germany, and Rome is usually even warmer. Rain is high probability in both places.

My choice would be a wind and water resistant long jacket with a hood, and a heavy sweater to wear under it.

Also a warm hat, scarf, and gloves.

You shouldn't have to upsize your suitcase. I travel a lot in the winter (Rhine Cruise + London last Christmas, London early this December, etc. ) I never have to use a larger bag. I take a space bag -- EMPTY on the way over -- and use it if I need more space in my bag for the flight home due to shopping or whatever. You can wear your puffer coat on the plane and throw it in the overhead. I usually take cashmere sweaters, both cardigans and pullovers since they are very light but still very warm and can layer them over blouses for more warmth.. Gloves, a hat and/or warm scarf, wool socks (I usually take cashmere blend but SmartWool or any other type are OK) either silk bottoms or tights and it is plenty. I don't usually take jeans but that is a personal preference. I prefer black or charcoal wool, wool blend, or knit slacks that can be dressed up or down. All will easily fit in a 22 incher with room to spare.