Last 3 cruises I did was on liberty of the seas. All 3 times were balcony cabins on deck 7 (doubt that it matters unless the suites are different), i've never slept on such a hard mattress in my life! To me it feels like an inch of padding on top of a sheet of plywood and i'm not being sarcastic.
I'll be on the Allure next month, I hope its better.