Honestly I think a lot comes down to understanding materials and some logic.

Natural materials tend to be desirable and can be combined and even bolstered with synthetics to make a nice blend. 98% cotton with 2% spandex for women's denim that has to stretch more? That's reasonable. But 12%? Adding in some random 15% polyester? That sounds like a combo that is trying to save money by cutting down on higher cost materials... Already a red flag.

As for logic, I have to ask myself, is the product I am holding trying to take advantage of a trend by "duping" an existing product? Like a thick fuzzy sock that gives the impression of a thick merino wool sock but is actually pure synthetics? I'm not trying to get down on synthetics here, they have their place, but it helps to ask-- what are they trying to lure me in with?

I know there is a lot we don't know... One company's bottom of the barrel cotton against beautiful long staple cotton are both still just going to be "100% cotton" on a label, but taking the time to look at a product in detail can help a lot.

Everyone has a different range for cold. I grew up in -50 celsius, so below zero I think offers more options... But that's me!

I'm quite happy with my Helly Hansen raincoat, it's long and cute.

I'm going to take a different direction here and say that if you're sweating in your coat, you might be more interested in layers that fit well together. For example a nice mid layer vest that goes under a good shell jacket. That way you've got some temperature variability.

Also if you're paying in Euro you (probably) don't live somewhere that gets TOO cold. Versatility may be more important than being warm in - 50 celsius.