The problem with armor is that it's heavy and uncomfortable, but hundreds of years ago, people came up with a solution to help make wearing it bearable: the gambeson.  Essentially, it's like wearing a shirt/jacket made out of a quilt.  In fact, it's padding enough that poor people used to wear them as their only armor.

My gambeson is in fact made out of padded black moving blankets.  This provides adequite padding to prevent the leather and cast armor, as well as the chainmaille rings, from digging into my skin, if I were to only wear something as thin as a tshirt underneath.

I based my coat on a sewing pattern from McCall's: M2233 MISSES' AND MEN'S JACKET, SHIRT, APRON, PULL-ON PANTS, NECKERCHIEF AND HAT
from the UNIFORM ESSENTIALS collection.  I took the chef's jacket, but put the short sleeves from the shirt on it, and shortened it by several inches so that it came down just below belt level.  It ended up being a little baggier than I liked, so I also took in 2" from each side.  Instead of buttons down the front, I used 3 strips of 1.5" Velcro, oriented horizontally.  I ditched the pocket too.  The high mandarin collar is also perfect for protecting the neck from the gorget armor around it.

 

Can't you tell the similarities? 

I'll get some pictures up soon.  In the meantime, you can see it under the chainmaille, in those pictures.