This is a good question--
It's true that water doesn't weigh anything in water- in other words if your waders fill up with water it won't pull you down because the water in your waders is the same density as the water outside them--- but if you try and stand up out of the wader with your waders filled, it'll be like trying to walk around weighing 1,000 lbs--- this could cause a lot of problems if the only way out is up a steep bank.
One things a lot of folks do that fish where getting knocked down is a real possibility like the surf, or where a spill could be fatal due to hypothermia is to wear a water proof top of some sort and a belt cinched tightly over the jacket and waders (When surf fishing or steelheading on dangerous rivers I use one of those web belts scuba divers use to attach weights (umm without the weights
it ran something like $6-7.00) I've had waves break over me, gotten knocked off rocks and stepped in a hole one time following a fish steelheading and went in over my head--- but just got maybe a cupful of water down my neck each time.
So, depending where you fish, and how steady you tend to be on your feet, you might want to consider some/any of these--- or at the very least you should know that this stuff is out there:
-a wading staff like Folstaff that attaches out of the way to your belt and folds out when you need it,
-Studded wading shoes offer a more secure grip on slimy bottoms--- but tear up a drift boat. Some brands of wading boots like Korkers offer interchangeable soles.
-Korkers also offer a couple models of lace or strap on "soles" with carbide spikes that go over your wading shoes. These are much longer and offer a much better grip than regular studded soles. These are way overkill on most waters, but there are some areas like the rocks at Montauk NY, and some winter steelhead rivers with slick rocks and high flows like Salmon River, NY
where they are standard equipment to reduce the chance of serious injury
- wading belt that can be tightly cinched over your waders
-water proof top under your vest that goes over your waders and is cinched down with a wading belt
- any of these and a pair of inflatable suspenders. These can be ones you inflate yourself by blowing on a tube, or self inflating ones that activate usually after being in water for 5 seconds. These are convenient in that they don't incumber your movement the way that a life preserver would. And the self inflating ones are designed so they activate in the event you are knocked unconscious etc. ( A guy at Montauk was wearing one a week or so a go and was knocked down by a wave. He was fine, but didn't get back up fast enough to prevent the thing from deploying and had to take a lot of ribbing from his buddies. )
Again, many of these may be way overkill for the waters you fish. However there have been several fatal drownings this year, one was a guide on the Snake that was wearing waders but no pfd when his boat flipped, and several very experienced surf fishermen, one just recently on Cape Cod that was wearing waders, belt and dry top (but no pfd) that was swept off a sandbar at night--- so there are definitely areas that warrant special consideration because of some serious conditions.
And since you're in Michigan, one thing you should definitely do if you chase steelhead in the winter, is to keep a heavy blanket and a change of clothes in the truck to change into in the event you do take a spill and take on some water. The same spill that might just be a little embarrassing in the summer could be a real problem in winter because of hypothermia.