I went with my mother to the budget German supermarket, Lidl. There are always lots of interesting things on offer there.
Lidl was selling cheap men's slippers. My mother bought me a pair to wear when I visit her house. They reminded me of the sort of slippers that you can buy in practically every convenience store in Japan.
Personally, I don't believe it is necessary to provide slippers for guests, but if you do, those slippers would be a good, affordable choice.