My daughter loves the look of IKEA's Hemnes Day Bed and it looks like it ticks all my boxes for practicality. But looking at the mattress sizing and reviews it looks like it might only fit an 80cm mattress. Her current mattress is 90cm and really good for her back. Does anyone have experience of these beds and can advise if its a 'roomy' 80cm or will her 90cm mattress will be an impossible squeeze?