Ikea is now offering 365 days to return any product - even assembled - but still in resellable condition (unless there the reason for return is defect)
From their website:
365 days to change your mind
Too big? Too small? Too something else? If you’re not completely satisfied, or simply just change your mind, you can return your products within 365 days. You can return any product, even if you assembled it, as long as it’s in unused and in re-saleable condition. Please provide proof of purchase and, if possible, the packaging.
We will refund you by the same method as your original payment. If the returns criteria are not fully met, IKEA reserves the right to refuse a return (or exchange) or offer a refund card only. Government photo ID may be required.
Love it or exchange it (your new mattress in 365 days)
It takes time for you and your new mattress to get used to each other. That's why we give you 365 days to be sure you're compatible. If the chemistry isn't right, simply come back and choose another mattress. When you've found your perfect match, you can sleep easy for years to come with our free 25-year warranty.
Click HERE to read the full Terms and Conditions.