First, copolymer is really nothing special or different. All monofilament lines, mean a line that is a single (hence mono) filament are copolymer lines. There are a dozens, maybe hundreds of different nylon polymers that range in properties from super soft and limp but very stretchy and prone to breakage and abrasion to very hard and stiff where they can be so brittle it's almost like cooked spaghetti. Copolymer line take two or more of these polymers with different properties and blends them to make a line that is not achievable with a single nylon polymer and draws it into a single, clear (or colored) filament.
Fluoro is not nylon though it looks similar. Because there are also multiple polymers of fluorocarbon, it may/may not fish little stiffer and stretch more or less while shedding water similar to nylon monos.
Deep water screams for a superline but I get the freezing thing. It does help if you use a fused superline like FireLine, Nanofil, Sufix Fuse, etc. because they're smoother on the surface of the line and shed water better.Over time they will wear and get a little "fuzzy" which will not reduce line strength but it will start to collect more water. I've used a ton of Nanofil and have taken to giving the business end an occasional wipe with some silicone fly line treatment to help keep water running off. It works but has to be re-applied with use, you'll know when it's time.
Like just about everything else in life it's all about the trade-off you're will to live with.