Hi Mills1428,
I don’t think there is a “norm” and each retailer or manufacturer can have a different policy and this would be part of each person’s personal value equation.
The cost of a return (or exchange policy) is built into the cost of the mattress and some retailers or manufacturers don’t allow returns at all (it would be less important for a local purchase that you can test than it would for an online purchase that you can’t test ahead of time).
I think for most people 30 days would be enough time to decide if a mattress is a good “match” for you in terms of PPP.
Phoenix