Hello Liam. I have been fly fishing in Western Washington for 45+ years. I live south of Puyallup and am fortunate to live 25 to 45 minutes from some good Puget Sound beaches (Sea Run Coastal Cutthroat, Resident Coho & Jack Chinook), and less than 1 hour equidistant from four different lowland & moderate to high gradient mountain river systems that all have resident native Coastal Cutthroat Trout.
I fish year-round; salt beaches and year-round trout streams in late fall to early spring. I have the CFS scoped out for the (year-round) rivers I like to fish and actually get USGS water data service emails when the level for each of the rivers begin to clear and drop to what I can safely wade. I never fish rivers without a telescoping & folding wading staff (trekking pole) that fits into a (tactical) belt pouch, with a retractable lanyard.
Our air temps usually don’t get that cold, but our marine humidity with water temps in the low 40s chill me to the bone. Late fall - mid-spring I wear “breathable” (?) stocking foot chest waders for warmth with wading boots and neoprene leggings for both warmth, and padding-abrasion resistance. When water levels drop during those week-long dry winter cold snaps into the teens-mid 20s I wear stocking foot guide weight neoprene waders. In early fall and late spring I wear pant waders and the leggings.
As the air & water temps warm I wet-wade with durable, abrasion-resistant, and surprisingly fast drying OCP trousers, midweight hiking socks, neoprene socks, wading boots with studded or bar cleat rubber soles, and neoprene leggings. If I am hiking in over 3/4 mile, I’ll use hiking soles on my (Korkers) boots and change to studded or bar cleat rubber soles when I begin wading. I bring extra pairs of wool and neoprene socks to change into if the hike out will also be long.
A form fitting wetsuit would be nice for the decreased drag in the current, but IMHO that’s about it. In the late spring, summer, and early fall it would be waaay overkill. In winter, getting in and out of it would be difficult, and cold.