Approach it by understanding what keeps you warm. That factor is all about trapping the heat your body produces in very small air spaces. Down feathers can do that, fluffy fleece blankets can, fiber filled blankets can as well. Natural wool fibers also have that ability.
A down blanket has to have a very tight fabric covering to prevent the feathers from escaping but that fabric is not good at absorbing moisture from your body so you can end up feeling damp and sweaty. Being damp makes you feel cold. That is where a combination of fleece next to your body to absorb the moisture and either a natural or synthetic down blanket over that helps keep you warmer. As fleece blankets are easy to wash and dry and down not quite as easy it means laundry day is easy. You wash the fleece more often because the down blanket does not then need frequent washing as it is not getting moisture from your body on it. In winter my “sheets”, both bottom and top layer are fleece. You can purchase 50” or so wide fleece at fabric stores. Basically no sewing is needed to turn it into a blanket and the choice of colors and patterns is quite extensive. The “Luxe” in-house brand from Joanne Fabrics is by far the thickest and softest of the fleece by the yard that I have found. It cost more but is worth the extra price as it is warmer and softer. Walmart also sells fleece by the yard in the fabric department.
Thrift stores generally have fleece blankets in decent condition.
I personally do not like wool blankets as wool really makes my face itch when it contacts it, even the softest of wool. Wool is very warm, no question about that. When it is really cold I wear thick wool socks to bed, it does not make my feet itch, and they makes a huge difference in feeling warm all over. Sometimes I wear gloves to bed on really cold nights as I tend to have my hands out from under the covers. Of course my gloves have touch screen fingertips if I am watching videos on my tablet while also staying warm under the covers.