I am off to Edinbrugh on Friday...what would be best to pack?

Basically I know its likely to be slightly chillier than where I am (Cardiff) but kinda wanted to pack light thus avoiding taking a HUGE suitcase as am staying at a friends and don't want to take over! I am going for 6 days and the weather looks like its going to be raining...any suggestions as don't want to freeze but also don't want to be stuck with a case I cannot move.