Blanket shirts can be homemade or purchased. YouTube has numerous videos on making your own.
Perhaps the best known commercially available blanket shirt is the Boreal Shirt from Empire Canvas Works or Lester River Bushcraft. They are premium pieces of clothing and priced accordingly.
If your budget doesn't permit spending the money for a Boreal Shirt, or if you want to try out a less expensive factory-sewn option check out the Jämä Blanket Shirt from Varusteleka. They are sewn in Varusteleka's factory in Helsinki, Finland.
Varusteleka currently lists two variants, one made from H.R. Co. blankets, while the other is made from Finnish suplus wool cloth that was used for their M/65 uniforms.
A couple weeks ago I bought one in the Finnish wool, and I used it for the first time on my recent deer hunting trip while hanging out in our cold cabin. I wore it over a Hill People Gear long sleeve base layer, a flannel shirt, and an Orvis fleece and wool vest. I was warm in the cabin where the temps were in the low 30s. It wasn't very windy outside and the Jämä shirt kept me warm when I stepped outside for a few minutes to take a leak. If you're going to wear this in windy conditions, you're going to want a shell over top of it, however. A suitably sized windproof smock would be just the ticket.
For size reference, I am about 5'5" with an 18" neck, 32" sleeves, a 45" chest, 48" gut (ugh), and normally wear an XL or 2XL, depending on the item of clothing or a brand's sizing. The Jämä Blanket Shirt that I bought is a 3XL. (Pay attention to Varusteleka's sizing guidelines.) Since the garment does not stretch and you need to pull it on, it needs to be big, especially if you have any layers on.
The sleeves are 35" long, so they cover up my hands. I can roll them up if I am working.
Obviously, this is not something I'd wear about town. If I'm out in the woods I don't care if I look like a wannabe Jedi or I'm on my way to Mordor.
The hood is a bit floppy. In the picture I am wearing a ball cap under it, which keeps it out of my eyes. It's deep enough to provide protection against wind from the side and to help create a warm air bubble in front of your face.
As shown in the pictures, it has a kangaroo pocket, hood, and the back is longer than the front. I like the vertical placement of the front pocket, which is large enough to comfortably hold my keys, a pair of rag wool gloves, and my iPhone 7 Plus.
There is a smaller pocket inside the kangaroo pocket. You could put a folding knife in there but I don't see myself getting much use out of it. It's not large enough for the iPhone 7 Plus.
The stitching is good quality. There were no loose threads. The wool fabric is a bit nicer than an old military surplus blanket, which makes sense since it was actually intended for use in making clothing. It's about the same weight as the old USGI M-1951 wool field shirts but not as scratchy.
It's a good, basic hoodie. Compared with the Boreal Shirt it lacks some features. E.g., a draw cord on the hood, an adjustable collar, and snaps or straps to cinch down the wrists. However, the Jämä shirt also about 1/3 the cost. If you have moderate tailoring skills you could customize it.
Do I recommend the Jämä wool blanket shirt? Yes, if the sizing and feature set work for you. IMO it would be great for bow hunting with temps in the 30s or 40s.