Both the SweetNight and Siena are manufactured overseas, and the materials/foam quality at this price point can be a concern. Novilla’s mattresses are also primarily manufactured in Indonesia.
I understand that your budget is pretty restrictive, but I would focus less on the brand’s online reviews and more on the quality and durability of the materials used. Even at the budget end of the market, there are some better options from manufacturers that use higher-quality foams and springs.
If you can stretch your budget a little, I would look at something made in the USA, such as the @Sleep_EZ Essential mattress, which is one of the best values in a latex mattress.
You could also look at @EngineeredSleep and their Today Mattress, or the Brooklyn Bedding CopperFlex / CopperFlex Essential. If you are in the Illinois area, @BeloitMattress and their Foam Royal mattress would also be worth considering.
For a back sleeper around your weight, I would have more confidence in the construction, materials, and potential durability of these options than in the very inexpensive mattresses you are currently considering.
With a $600 queen-size budget, though, you will probably have to compromise somewhat on either material quality, durability, or your preferred feel. If possible, I would try to stretch the budget a little. All of the mattresses mentioned above are made in the USA and offer, in my opinion, better quality and durability than many of the foreign-made mattresses you were looking at.
If you are only going to use the mattress for about 9 months and aren’t too interested in long-term quality or comfort, then any of the three mattresses you mentioned may make it through that time frame just fine.
And if I’m being honest, a queen mattress at or under $600 is not impossible, but it is a more difficult task. At this level, I would focus less on the issue of whether the mattress can be returned and more on what are the best materials I can get for my money?
A good return policy is certainly useful, but it doesn’t make up for poor-quality materials.
Maverick