Hi loxanna
Welcome to our forum and thank you for your kind words. 
Iām not sure what youāve read aside from the mattress shopping tutorial which is indeed the first place to start your research, just in case you havenāt read these yet two of the most important links in the tutorial that I would especially make sure youāve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best āmatchā for your son in terms of ācomfortā, firmness, and PPP (Posture and alignment, Pressure relief, and his own Personal preferences) that can help you assess and minimize the risks of making a choice that doesnāt turn out as well as you hoped for and post #13 here which has more about the most important parts of the āvalueā of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesnāt turn out as well as you hoped for).
As your local area mattress shopping options are so limited you can easily find online options that fit your budget range and ship nationwide. Some of the better online options I am aware of and I consider to be good quality for value, which are also our trusted members and are listed in post #21 here and who are all very experienced and knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex and memory foam and other options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
In addition to the online members of the site listed in the previous membership link ⦠post #12 here has some of the better online memory foam options for those who are looking for a memory foam mattress.
For those that have a more restricted budget then post #4 here and the posts it links to also include many of the better lower budget online options Iām aware of as well.
Posts #1 and #2 in this topic also includes more information about the new "breedā of āsimplified choiceā mattresses (aka āone choice fits allā or āuniversal comfortā or ābed in a boxā or ādisruptorā or āmillennialā mattresses) that are available online as well that are typically in a budget range of between $600 and $1000 (queen size).
While I can certainly help with āhowā to choose ⦠Itās not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first āruleā of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best āmatchā for you in terms of ācomfortā, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will āfeelā to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or ātheory at a distanceā that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
Side sleepers in general tend to need a softer mattress than back or stomach sleepers and an online retailer will generally suggest a mattress that they believe will have the best chance for success (based on averages) since a return is very costly to an online retailer or manufacturer and itās in their best interests to make a suggestion that they believe will have the least possible chance of being returned.
Dust allergies would more of a concern with keeping a healthy clean environment make sure he uses a good mattress pad and a newer pillow, and that he washes his sheets frequently and that he vacuums around his sleeping area.
As you may be aware, Dreamfoam is a member of this site which means that I think very highly of them and that I believe that they compete well with thebest in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration. The Arctic Dreams certainly represents one of the better value option for your specific needs.
Hopefully this gives you good information, it looks like you are on a good track and Iāll be interesting to learn what you decide to do.
Phoenix