Given the OP mentioned her lack of options, encouraging her to buy something good quality which will not only build her wardrobe but bring longevity too. As such, o's more than sensible to recommend brands that wear well, not only in terms of quality, but aren't trend-led.
For the record, yes, I love Cos, but do you know something, I don't and have never bought or even tried on any of their draped dresses. The brand makes great basics, indeed, their new strap line is 'everyday luxury', so if I was looking to build/add to my wardrobe with a good pair of jeans, a great t-shirt/blouse/top, a dress, a new jacket, I would start there. However, although it isn't right for OP, maybe someone else in a similar position might rethink and give Cos a try - this thread rather shows that many posters don't know the brand as well as they think they do.
Good luck OP, I hope you find something. I honestly don't think it's a problem if you wear jeans even if you're wearing them during the day. Jeans are the workhorse of my wardrobe, as are nice tops. By the latter, I mean a variety of blouses, shirts, sweaters. Indeed, anything worn on the top half. But, only you can decide what is a nice top. I recommend looking on Pinterest or online for french girl style and nice tops/jeans - the french, particularly Parisians do this very well. H&M might, and should turn up a good option, as will John Lewis.