So far one of my warmest jumpers has been this one by Project social T. Its fleece lined and so soft and the neck line allows you to have it off one should too (like I do just for a more personalized style).
So I recently got my boyfriend a raglan style jumper from boohoo. He made the mistake of letting me try it on.... it is so warm and fluffy. I think it will become mine soon. It was a great price at £15 and they always have deals on with things such as delivery and discount codes.