I bought this Marimekko dress almost by accident last winter when I was pregnant.
Impulse shopping is not always just an unwise way to spend money, stuff up your wardrobe and destroy the planet - sometimes it can lead to very useful pieces. I don't actually do that much of impulse shopping, but I have some items that I have bought without planing to do so ahead or giving it that much pre-thought. And in my case those have often turned out to be pieces I really use a lot.

I got the dress in the largest sie they had, as I wanted it to fit my belly all the way.  I could have managed with a few sizes less in the end too I noticed, but this is the kind of dress that looks pretty much the same in all sizes and it still works belted for a normal belly as well. And it buttons up for nursing. So I've been able to wear it still, around the year. Well worth it's Marimekko price.

But a thin cotton dress worn just like that won't of course work on it's own most of the year up here in the North. It would get too cold.

As it is among my most linked posts I think you remember me writing about winterizing summer dresses
, and the importance of layering and layering again; the anatomy of dressing when really really cold. Here's the winter dressing post for this year then!
If you wear a cotton dress in winter the dress is merely a detail, kind of an acessory, a coating to what you actually wear. It's what underneath that counts. And on top too, as you have to be able to take something off when you go inside in order not to melt down to a pool of sweat (we have quite stiff heating over here and tripple windows) - cardigan(s), the coat (preferably of the longer kind if you wear something like this), socks and boots and so on yadi yadi.

So, under the dress I have an underskirt. It is mostly for "cosmetic" reasons, to prevent the cotton dress from sticking to the rest and looking all weird. It's not really that warming. But every layer counts.

Underneath that I have another dress! Stretchy, tight, comfy and in cotton. (This one with a nursing pocket in front too which comes in handy at these baby times.)  If you are of the kind that gets real freezy add a slip or top underneath still.

Wearing double stockings also warms up. Or tights plus stockings. But for me one pair of thick stockings (mainly wool or knitted cotton) usually is enough, as far as the mercury stays above minus ten c. But here's the little important trick! People always joke about grannies and their wool pants. But that's what keeps the warmth! You can actually get those from somewhere, but a pair of hot pants or so works just as well. I have some wool stockings of which I have cut the legs off. Comfier and easier to do it that way adding high socks to go, than stuffing two pairs of stockings onto each other.

So that's it! Out to fight the cold in a summer dress, no prob!
(If you're going to go all smartass and say "why not just wear trousers" then think again, you can only stuff so many layers into a pair of pants, but when it comes to a dress, options are pretty much endless. I actually find it warmer in skirts and dresses!)