@jools could have sworn you said you bought new ones but if I'm mistaken then there's nothing stopping you from doing so. Why wear anything that is old, worn out and unattractive?
I did but I got el cheapo ones and they're a)too baggy and fall down; b)too thin so not very warm. I've had to resort to my old ones but I figure no one else sees them (especially not on 365!) so it doesn't matter.