I have a cariboo :)
With my summer daughter I just used cotton sheeting from a baby store I guess, and if I ran out of the bassinet ones just folded up a cot sheet in quarters, and chucked a lightweight fleece on top.
This time, we are having a winterish boy, and finances are a little more on our side, so I did a wee bit of shopping and crafting. I made a couple of fitted fleece sheets, and a couple of flannette flat ones, and purchased a top rug from these guys:
Wool Rug People
I will use a cot waffle weave rug folded into quarters if need be as well, it's hanging around as a spare. Pillow cases are also awesome bottom sheets for the cariboo

Just slip the mattress inside