Hi cole308,
The first thing I would suggest is to read post #1 here which along with the information it links to is the most important post on the forum. It will give you all the information you need to make good choices including links to some guidelines that will help you test mattress as objectively as possible so you have better odds of making a choice that is suitable for your body type and sleeping positions. It will also give you some general insights into the type of mattress that is generally most suitable for a stomach sleeper which is the most risky of all the sleeping positions for alignment and back issues. The general “rule” is that the thinnest firmest comfort layer that relieves pressure in your most pressure prone position (other than stomach if you sleep in other positions as well) is the “safest” choice because you will be closer to the support layers which will help you stay in better alignment and will be better for your back.
One of the links there also goes to the mattress shopping guidelines here and the second guideline is to make sure that you know the details of every layer of the mattress. If you post them here I may be able to give you some insights into the mattresses you are looking at.
I would pay little attention to warranties because they only cover defects in construction and don’t cover the loss of comfort or support of a mattress which is the main reason people generally need to replace a mattress. As you can read in post #4 here … warranties have little to do with how long a mattress will last for you.
I would also not pay a lot of attention to mattress reviews that talk about how comfortable or uncomfortable a mattress may be for other people. Each of us is unique and your own objective testing will tell you more about what you need and prefer than other people’s choices. A mattress that is “perfect” for one person may be completely unsuitable for another with a different body type, sleeping style, or preferences and one person’s “too soft” can be another person’s “too firm”. Reviews are most useful to help you know the quality of the service or other information about the retailer or manufacturer selling the mattress. You can read more about the benefits of reviews in post #4 here.
You can read more about the pros and cons of latex here and about memory foam here but thick comfort layers of soft foam in either material could be particularly risky for you being a stomach sleeper and possibly more so with memory foam because it tends to “creep” (gets softer) over the course of the night so you may start off with god alignment but by the time you wake up you may be out of alignment. Gel memory foam is generally a little better with this than regular memory foam.
Latex is also the most breathable and coolest of the three different types of foam materials (latex, memory foam, polyfoam) but the foam in a mattress is only part of what helps to control the temperature. You can read more about the different factors that are involved in the sleeping temperature of a mattress in post #2 here and some of the other posts it links to.
Once you have confirmed that both mattresses are likely to be suitable for you (not just comfortable in a showroom) … then deciding between them is an individual preference based on all the tradeoffs that are the most important parts of your personal value equation which includes the quality, value, and benefits of each mattress, your confidence that a mattress will be suitable for you in the long term, and all the other parts of every mattress purchase that are most important to you (including things like exchange policies). If you are looking at two roughly equal choices … I would lean towards the firmer one. I would also buy a mattress as if you only had one chance to buy the right one and had no chance to return or exchange it after the purchase. In other words I would put much more thought into how suitable a mattress is than what to do if it isn’t. This will help you make the best possible choice and an exchange policy can be a backup instead of a primary reason to buy a mattress.
Other than your basic needs which are pressure relief and support/alignment … most of the rest of your purchase will be based on all your many personal preferences and circumstances which means that only you can decide which are most important or at least the “least risky” to you once you are confident that the basic needs are covered. All of this is to help you eliminate the worst choices and help you know “how” to choose between the better ones so that you can have more confidence about “what” to choose based on your own personal value equation.
Phoenix