Hi TMUirs,
There is more about the “value” of a mattress purchase in post #13 here and as you can see the most important part of any purchase is how well a mattress matches your specific needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). If you can’t test a mattress in person then the best way to choose would be with a more detailed conversation with a knowledgeable and experienced online retailer or manufacturer who is more interested in selling you the “right” mattress then they are in selling you anything you are willing to buy. If a mattress is too soft or firm for you and you can’t sleep well on it then no matter what you paid it would have little value to you.
After PPP … the most important part of a mattress purchase is the quality of the materials inside the mattress. While any mattress in the budget range you are looking at would use relatively low quality materials inside it … I would still want to know what they are (see this article) so you can compare the materials to the guidelines here. If the materials are very low quality and the mattress for example is already “on the edge” of being too soft for you then you may not even make it through the initial break in and adjustment period of the mattress in the first few weeks before foam softening results in the loss of comfort and support that takes you over the edge and the mattress is no longer a suitable match for you. It certainly wouldn’t be my first choice unless you can find out the information you need to make a more informed choice and you you are confident that a retailer or manufacturer really does have the quality of your sleep and your best interests in mind.
I’m not sure what your budget range is but some of the better options and possibilities I’m aware of in the lowest budget ranges are listed in post #4 here that would certainly be well worth considering. While the price of a mattress is certainly an important consideration of course … I wouldn’t buy any mattress no matter what the price there is a high risk of compromising the quality of your sleep because in many cases the “cheapest price” can be the “worst value”.
I also don’t know how tall you are but it may also be worth considering a twin XL which is 80" long vs a regular twin which is only 75" long.
This is more of an issue with some memory foam mattresses than it would be with polyfoam but if your mattress is CertiPure certified or made in North America then any “new” smell with a mattress wouldn’t be an issue for most people that aren’t unusually sensitive and should dissipate fairly quickly.
Phoenix