Hi 2sp I get the same ones every year from Primark shoe dept. They make great sturdy slippers. They look like Ugg boots, You can get them in grey black and a tan colour. They cost £5 and last me all winter.
I have different microwaveable ones, where you take out rubber soles and heat them for 45 seconds then slip them back (a zip compartment between the inner and outer soles). Heat feet quickly.