Toddler mattress for a 2-5 year old. (Cainscross GL5)

Does anyone have a spare smaller mattress that might suit a child up to 5? eg something 140 long by 70 wide. It is to go on the floor for occasional use when my grandson comes to stay so I don't require the bed. It could be a little bit longer than 140cm as long as it isn't any wider than 70cm. Thank you