We got an Ikea one too. It's a wooden one which can be shortened then made longer into a full size single. As for sheets, we've just been using a flat cot sheet which is just big enough. We bought some single sheets on the weekend too so we'll use them next and just tuck them right in and under to fit until we lengthen the bed out. We have it shortened so it has just a gap in the middle of the sides where we've put a pillow for now but he seems to be fine with it anyway