Bottom sheets for odd sized sofa beds?

[PeazlyPops]

I have a clic clac sofa bed like this www.argos.co.uk/m/static/Product/partNumber/6916370.htm

I've been trying to find a fitted bottom sheet, but with no luck. It needs to be 105 x 182cm, any ideas where I could get this from?

ikea sheets are vailable in 100x200, maybe they stretch enough?
otherwise I would just use a normal double sheet and put the overhang towards the not so visible side.