Hi luxastraea,
30 days is normally enough to decide if you are sleeping well on a mattress and I certainly wouldn’t keep a mattress that causes you pain or discomfort when you sleep on it unless it’s too firm in which case you can add a topper. There would be little “value” in buying a mattress that you don’t sleep well on regardless of the price or even if it was free.
The cost of returning a mattress may also play a role in your choice as well.
You can see the costs involved in returning an Amazon fulfilled mattress through their large items return department in post #11 here.
If the Dynasty mattress is fulfilled by Amazon then you would be subject to the Amazon return policy not the Dynasty return policy.
If you are buying a Dynasty mattress from their own site and you need to return it you can see the details of their return policy here. As you mentioned you would be responsible for the cost of return shipping and which could be several hundred dollars since you won’t be able to recompress the mattress and use a courier to return it so any returns would be with a common carrier which is much more costly.
You would be lucky to receive 50% of your purchase cost if you are re-selling a used mattress on Amazon.
Phoenix