I don't know about sheepskin but SIL bought me a pair of woolen/fake/something or others from Marks and Spencer a couple of years ago and they are the warmest and most amazing things ever. And they'rethe first slippers I've ever had that don't make my feet sweat if I'm not wearing socks.
I assume M&S would continue the range, if slightly adapted, forever.
I bought these a few weeks ago (but for £21.00, not the £16 they are now). Really warm and snuggly but guess these more substantial ones will be even warmer. I've never ordered from Littlewoods before but was impressed by the service etc.