The company that made them is called Old Friend Footwear https://www.amazon.com/stores/page/935958D6-8EDA-4976-88D5-CA44EC3BDEFA
The ones I have are basically these but mine have a soft sole and the shoe strings and I don’t think they make that exact style anymore https://www.amazon.com/Old-Friend-Bootee-Slipper-Chestnut/dp/B008E9QFHG
I'm from the UK - here's the Amazon link for the one I purchased (not sure if it's available to the rest of the EU though or if it's for UK only)
https://www.amazon.co.uk/Sly-Trilogy-Move-Compatible-PS3/dp/B07VRM4FVH