This is just my opinion, but I have been a Superhost for 5+ years continuous now so I feel fairly qualified. I think you coddled the guest way too much by going overboard with providing all the cushions, etc. Entitled guests get one thing, and keep asking for more. Why would you interact with the guest so much and provide cushions? If they want something like this, they can go buy their own. I would have filed in my mind, 'one guest said the bed was uncomfortable.' Perhaps thank them for their opinion and say you might order a new one in the future, etc. NOT IMMEDIATELY. This is subjective - the weight of the guest determines how far they sink into the bed. If the mattress is old, yes, you might replace it before you even begin with Airbnb. But not instantly for one person! What are you going to do for the next guest, that says it's not firm enough, the one after that says it's so soft, and so on? Buy 100 mattresses and keep switching them out?
I don't have time to read reviews people write. I'm busy cleaning these checkouts. Don't worry about it. Keep on booking stays, the next person's review will bump that one further down on your review list. If you don't think it's moving down on your view list quick enough, dump your price and make it one night minimum stay.
I do the following: Before guests arrive, I send welcome messages preparing them for a great stay, providing instructions on arrival, and letting them know I want to be sure they have a 5* stay, so please let me know if anything isn't 100% so I can fix it right away. (this prepares them for satisfaction). Nobody ever asks for anything because I have prepared the units for every possible scenario at this point.
Inside, I have little sign preparing them for the upcoming 5* review and my Superhost status, and under it, a pen with a questionnaire in the units with a full sheet of paper that I have printed with a series of questions. Not all guests complete it but they see it, but when they do complete it, it provides them an outlet to vent opinions before the official review - but it also has provided me excellent ideas over the years to prepare the spaces to exactly what the guests want! It is invaluable! I have received great ideas, some not so great ones. A lot I never would have thought of myself.
After they depart, I send messages (nearly all messages are automated btw) requesting their 5* review. You have to put them in the frame of mind for the 5*. This is why you keep saying it. Reiterate the importance of it. I send several of these messages with variations until they leave the review. Staged out the day of departure, 2 days after, 5 days, 7 days, 9 days. At 2 weeks it expires so you want the review left before that time. There are multiple automation services to leave automessages, and I think Airbnb even offers one now. You want take advantage of it, because you get rated on response for Superhost.
I hope that is helpful.
