If you ever want to be less sure about a shopping decision than when you started researching, go ahead and read reviews for mattresses. Holy cow it's a mine field.
I don't leave reviews for anything, unless I personally know the person who sold it and I want to help them. So, keep in mind when you read reviews, it will be heavily biased towards the people that are unhappy about their purchase.
I had had a $1000 dollar mattress and it was ok. I needed to replace it after ten years, so I purchased at $225 mattress from AMZN. I figured, if I hate it, it's only $225, I can give it away and go to a mattress store. Four years later, it still works great. I have bought two twin mattresses for my girls too. No complaints.
It's $325 now, but I would buy it again if I needed to.
https://smile.amazon.com/gp/product/B006LAK9A4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I bought THIS mattress a few months ago. I was suffering from lower back pain every day, and my girlfriend suggested that it might be from sleeping on too soft of a mattress. My back pain was significantly reduced in as little as a few days (not completely gone, but a large part of that has to do with how much lifting I do at work). Strongly recommend.
Amazon. This changed my life.
I got this one from Amazon: https://www.amazon.com/dp/B006LAK9A4/ref=cm_sw_r_cp_api_glt_fabc_H0X7729P5CCBWT6KWDK9
I’ve had it for 1 year and 3 months and no issues at all so far.
i purchased it on amazon. https://www.amazon.com/Zinus-Ultima-Comfort-Memory-Mattress/dp/B006LAK9A4
https://www.amazon.com/gp/product/B006LAK9A4/ref=oh_aui_search_detailpage?ie=UTF8&th=1
It's lasted a year and a half and it's $231. That's already better time/$ than you got after the last one and it's not noticeably different than day 1.
You can get a new super, super comfy mattress for very cheap.
We have this one: https://www.amazon.com/gp/product/B006LAK9A4/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&th=1
My sister visited and we gave her our bed recently, she commented on how comfy it was.
We are on our second one bc the first one was for our van, second is for our apartment.
Some ideas:
I would encourage you to consider looking at this from a creative perspective.
It's an important need that you have a good mattress, so you can be well rested.
It's also important that you use this windfall in the best way for your future selves.
Imagine for a second if your family member, who has a very clean house, told you that they were upgrading from their very nice, comfy mattress to an even fancier, comfier mattress, because they just want extra fanciness.
They ask you, do you want our old clean, good, nice, but not super fancy mattress? I would say yes. I don't know what you would say.
People sell brand new mattresses every single day. Rich people upgrade for stupid reasons.
You may be thinking to yourself, I would never buy or sleep on a used mattress, that's disgusting.
Well, would you ever sleep on a bed in a hotel, or in an Airbnb? If you were visiting friends, would you sleep on a guest bed? Or even in someone else's bed, if the sheets and linens were all very clean?
When you buy a foam mattress online from Amazon or another company, it comes w/ a satisfaction guarantee. If decide you don't want it, and were to ask about returning it, they tell you to keep it, and send your money back. These mattresses get sold on craigslist.
If I were you, definitely get a good mattress if you need it. It sounds like you do.
But, I encourage you to be creative, strategic, and open minded about filling this need.
Maybe you can use $100 to get a used, clean, comfortable mattress, and put the other 84% into your emergnecy fund.
A night's sleep from a comfy mattress is good, and important. Sound sleep because of a well padded emergency fund is better.