Warm cozy shirt-jacket aka the "marmot ridgefield long sleeve flannel shirt" - Marmot Ridgefield Long Sleeve Flannel Shirt - Men's

I really recommend this shirt, especially if you layer and tend to be cold. It's cozy.
I've had it about a week now and have worn it much of the time. I have two other similar insulated shirts (famous brands I suppose lawyers don't want me to mention).
Good shirts...but this is the best, and I will likely order another Marmot next time I need one.

Comparing the three brands, this Marmot is the warmest and has the thickest insulation.
It is easy to get into because the arms have that slippery/satiny quilted lining so your arms don't get hindered, especially if you already have a sweater on for example.
Another brand's shirt exterior fabric is a wool blend while the Marmot is cotton flannel. I thought the wool would be superior but it is less windproof and not as warm as this one.
The hand pockets are also insulated and do the job nicely.

One thing about these shirts is that they aren't really meant to be tucked into your pants. You can do it but you'll be squeezed pretty hard, they are thick and you'd have to have really baggy pants to be comfortable. So you will likely wear it hanging loosely. It looks fine but there will be a draft from below -- and none of them seem to have a drawstring or similar feature. None of them have inside pockets for your cell phone or note pad or whatever. In an ideal world I'd want both features...but alas they aren't perfect but pretty close.

Cheers!