Vet bed gets full of hay & other bits - which are hard to get out, so I wouldn't use it. I also think it can be quite rough if they are prone to sore hocks.
If they are not chewers and the floor is actually too slippy for them, maybe try something like rubber backed indoor doormats / runners? They are often available cheaply from Aldi / Lidl / B&M / The Range, etc. They may be fine with it as it is, so I would wait and see.
Non-slip (ie hospital / wet room) lino would have been my preference - that's the type with a grippy surface, rather than raised ridges or circles.
