Hi songbird2012,
I’m glad you found us 
This should work well with or without a foundation. The spacing of the slats is important though …especially if you end up with a latex core mattress … but if the gaps are 3" or less then a solid foundation would be optional unless you buy a mattress as part of a “sleeping system” that you tested and is designed to work best with an “active” box spring in which case they should be purchased as a set.
[quote]I am female, 130 lbs and 5’5" and sleep alone
I have degenerative neck and shoulder issues, pinched nerves but no herniations.
I fall asleep on my side but move around a lot. I tend to curl up (sleep hot) and wake up with a stiff neck or my arm falls asleep.
I also have sinus problems and seasonal and household allergies.[/quote]
“Specs” about each person’s body type and sleeping position are an important part of how each person interacts with a mattress but there are many other variables as well. There are many different types of layering combinations that can perform equally well for people of a certain height and weight and sleeping style so the most “accurate” way to “fit” a mattress to each person is to work with a knowledgeable local person who has the experience and knowledge to help you make the most suitable choices in “real time” and in person. There are some general weight and height guidelines here and some general guidelines about sleeping positions here and some information about how different types of layering can change and affect these guidelines in this section of the site but these are general guidelines and starting points only and will do more to help you know who has the knowledge to help you make the best choices more than they can be used to design or recommend a specific mattress based on what I call “theory at a distance”.
If there are no good choices available locally … then the better online manufacturers are also very good at making more specific recommendations … especially if you have done some local testing and can give them some good feedback … because they know the specific details of every layer and component of the mattresses they make and sell and how they interact together. they also have a large customer base of people which have purchased the specific mattresses they sell which can be used as a reference point.
In other words … connecting with the experts who already know the specs and information that you would otherwise have to learn is much more effective than “becoming” an expert yourself or focusing on more technical details that can become overwhelming. With good help and guidance … your body and your “helper” will tell you which mattress is best for you.
There are also many aspects to sleeping cool and temperature regulation in a mattress and once again this will depend on how many different factors interact. There is more about this in post #2 here.
Allergies (as they relate to a mattress anyway) are usually connected to dust mites and mattresses that are less prone to this (good ventilation and humidity control and materials like latex and wool that are more resistant to dust mites along with a suitable mattress protector) would make good choices for those that are allergy prone. Humidity control and ventilation is one of the main “keys” to controlling dust mites in a mattress because they require humidity to thrive. Of course good protection that also deprives them of their “favorite” food source (dead skin) is also important. Again … an “expert” that already know this and is willing to give you the benefit of their knowledge can save you a great deal of time and research beyond the “basics” that can help you recognize which of the outlets you are dealing with really does know what they are talking about.
Post #10 here has a step by step process that can dramatically increase your odds of finding your “ideal” mattress that has better quality and value than anythin you are likely to find with a major brand or typical mass market outlet.
It appears from your comments that you may have already read this but the list of manufacturers and outlets that are the better options and possibilities in and around your area are in post #4 here centered on Trenton. There is also a more “categorized” list with more detailed descriptions of many of them in Post #7 here.
I haven’t talked with them so I don’t know about the level of knowledge, experience, or service they may have or their ability and willingness to provide the quality specs of the mattresses they sell (which of course wouldn’t be possible with their mainstream mattresses which I would ignore). If I was shopping there … I would be most interested in their Paramount mattresses, the Simmons Natural Care (one of the few major brands that is generally worth considering) and their Gold Bond. All of these though are dependent on their willingness and ability to give you meaningful specs about each mattress.
You will need a good mattress protector or encasement yes but which you use would depend on your preferences and the tradeoffs that were most important to you. The most common choice is a protector like the protec-a-bed or Luna which has a breathable/waterproof layer which is waterproof, semi-breathable, and for most people has little effect on the feel of their mattress. Other options would include a stretch knit cotton protector which is not waterproof or water resistant but is highly breathable and hyas little effect on the feel of the mattress. Another would be a wool protector which is water resistent (not waterproof), very breathable and temperature regulating, but will have some effect on the feel of the mattress. Choosing the “next level up” of thickness which is a mattress pad would depend on how much you wanted to change the feel and performance of your new mattress. There is more about this in post #10 here.
If you have just a basic or inexpensive mattress protector or mattress pad … then I would replace it. If it is a higher quality or cost protector or pad such as wool with a natural cotton cover, and it is the type you want to use with your new mattress, then for me replacing it would depend on its age, condition, and quality.
Hope this helps
Phoenix