Hi Astroaurora.
For starters, if you are working with a more restricted budget, post #4 here and the posts it links to also include many of the better lower budget online options I’m aware of (I’d just take into account the price point increases the mattress industry experienced during covid and shortages). Generally, Zinus or any mattress that uses low-density memory foam mattress and questionable or undisclosed FR solutions would not be on that list. If you have a little time to spare, I’d rather take the DIY approach, research, and ask for some guidance from a trusted, knowledgeable, and experienced manufacturer to ensure that whatever you chose is suitable for your needs and preferences. This may be a longer road but it avoids some of the common pitfalls of trial and error that most uninformed consumers go through and IMO it has the best chance of success especially for people wanting low-budget, safe, and more durable mattress options.
It’s certainly not unusual to see fiberglass in an inherent fire barrier either by itself or in combination with other materials ( see here for an example) and it can be used as part of the quilting in the cover or as a sock that encloses the foam layers in a mattress. There is some fairly detailed and technical information about fiberglass inherent fire barriers in this patent application although this is probably more technical than you may want to know. It is a “non-chemical” fire barrier and for most people, it would be “safe enough” although some people may have issues with the possibility (probably quite low in most mattresses) of some of the very fine fiberglass particles migrating through the mattress and being inhaled.
You can read a bit more about and flame-retardant methods that are “safer” in post #2 here and post #4 here to make sure that you are well informed and able to ask some poignant questions before making a mattress purchase.
Compressed wool, for example, is a very popular method of “natural” compliance and if done right there is no doubt it can be an effective method of complying with the fire code. Wool and other natural fibers are very breathable and provide an excellent microclimate and temperature control but the downside of thick compressed wool used as a fire barrier is that it can significantly add to the firmness of a softer comfort layer and reduce its ability to form a cradle.
Depending on the size of the mattress you are looking at, your specific stats, and particular needs and preferences you may still find products that are lower in budget and using good quality materials and safe FR solutions The smaller mattress companies and businesses that have the consumer’s best interest at heart are typically completely transparent about what is in their mattresses and take much pride in offering safe and time-tested FR solutions and even quality components sometimes in some of their lower budgets.
One of the Trusted members that quickly comes to mind is Arizona Premium that offers a good value/quality twin sloid core latex mattress. You can also apply the TMU discount to reduce the cost. I’d certainly peruse through our Trusted members directory to see what safe low budget mattress options they have. At least you can rest assured that you won’t find “surprises” down the road and they will carefully listen to your criteria for a mattress before making any recommendations.
Overall, the best advice I can offer you before you go down the “rabbit hole” of looking for the “cheapest” mattresses you can find, would be to read the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice, and perhaps, more importantly, know how and why to avoid the worst ones.
We’ll be on standby to answer any questions you may have on your mattress journey.
Phoenix