Quintessentially British.

Puffer Vests or Gilets, whatever you want to call them are the best. I used to wear mine (Navy Jack Wills Dudmaston) ALL the time. They go great over J. Crew tissue tees on a chilly day or over a sweatshirt on a cold day. For the ultimate lounge wear indulge in Aubin and Wills cashmere track pants, some rugby socks, and a tissue tee then layer in your Gilet.  Get one that fits snugly, but has enough room for a sweatshirt.. And good pockets are a MUST. - Bonus to the Jack Wills one? Built in headphone cable tidys and loops! 

Jack Wills Birchfield Gilet