This can be difficult because you might invest in an expensive cat bed but the cat is determined to sleep on top of the wardrobe. If this is a new cat I suggest you get something that is easy and quick to clean. In fact most cats seem to prefer sleeping on clean laundry.
You might also consider a special cat shelter that the cat limbs into and can feel secure in.
On the other hand a simple large cardboard box with a couple of pieces of your old clothing will also probably suffice.