Cardiff … as cupra says, you’ll not go far wrong with an AlpKit Hunka BUT are you planning on using a tarp of some description too?
Hunka’s could be thought of as a waterproof / breathable sleeping bag cover, ie, you’re not fully enclosed so with no tarp you’ll have to be careful in the rain but with a tarp you’ll be fine.
If you want something that you can fully enclose yourself in (Alpine style bag) and you’re on a budget then look at a RAB Storm. If you’re not on a budget, look at something like a RAB eVent superlight.