Hi niroth,
My first suggestion would be to make sure you have read post #1 here which has the information, steps, and guidelines you will need to maker the best possible choices.
I don’t keep a record of the refund policies of various manufacturers or retailers but most of them will have it on their website or provide the information with a phone call.
I’m personally not a great fan of refund policies for local purchases because of the extra cost it adds to a mattress (and the sale techniques it encourages) and prefer good and more objective testing. I do like some of the policies of many local manufacturers though who will open up a mattress (or some have zip covers which allow for easy access to the layers) and make fine tuning adjustments at a very reasonable cost if it’s necessary.
Online is a different matter because you cant test a mattress first so a good refund and return policy can add value to an online mattress purchase and reduce the risk of buying a mattress that you can’t test ahead of time.
You are fortunate to be in Boston because there are some very good options available there. the better ones I’m aware of are listed in post #2 here there are some links to posts and threads with comments and feedback about many of them in post #2 here as well.
Some of the members of this site that sell online are listed in post #21 here and many of these also have good return and refund policies.
While it’s important to buy a suitable mattress that has good PPP (Pressure relief, Posture and alignment, and Personal preferences) … it’s just as important to make sure that a suitable mattress also uses good quality materials because lower quality foams and components will soften and degrade more quickly and the loss of comfort or support that goes with this isn’t covered by a warranty. You can read more in post #2 here and post #5 here about all the many factors that make for the “best” mattress purchase for any particular person depending on which parts of their personal personal value equation is most important to them.
Costco are not what I would call “mattress people” and they know little about the mattresses they sell so you are really rolling the dice when you buy from them unless you are able to find out what is in the mattress you are buying. You can read more of my thoughts about Costco and the big box stores in post #4 here (also in reply to someone in the Boston area).
My personal preference would always be to deal with knowledgeable retailers or manufacturers that can provide you with much better information and guidance and where you can know the quality and value of what you are buying.
Phoenix