There are not a lot of factory direct outlets right in your general area but there are some a little further away. Post #2 here has a list centered on Savannah and includes a list for Charleston, SC and Columbia, SC. post 2 here has a list centered on Greenville. I didn’t originally include Mattress Hero which is owned by Park Place in the list because I thought they were only online but I just added them as it seems from your comments that they may have a local outlet?
I believe it is always better to test a mattress in person whenever possible as personal experience is always more accurate than “theory at a distance” and you have some very good choices in the large area you gave me.
The Couture mattress uses good quality memory foam and the price seems to be very good (depending on the size your price referred to). They don’t give the specs of the support layers but preserve is a CertiPur approved foam made by Hickory Springs and is also good quality. Of course if the layers are not correct for your needs and preferences then no matter how good the materials the mattress wouldn’t be suitable so taking your time (fully relaxed and at least 15 minutes) to test specifically for pressure relief and alignment is important. I would avoid making any choices based on the “overall feel” of a mattress. Always test for pressure points and for any tension in your back caused by poor alignment.
Both of you are lighter weight and primarily side sleepers which means that a comfort layer “in the range” of 3-4" would likely work well. It seems that you are locked in to memory foam but if you’re not it would also be well worth testing latex in your comfort layers or even other materials as well (latex over polyfoam or an innerspring can make a great mattress). Thinner comfort layers are preferable to thicker with memory foam especially (as long as it is thick enough to relieve pressure on your side) as it is the least supportive of all foams and a layer that is too thick for your needs can lead to poor alignment.
I would never consider a Sleep Number mattress and this article explains why I believe they are such a poor choice.
I would also not consider a 3 lb memory foam as they are not durable no matter how good they may feel in a showroom.
Tempurpedics are a good quality memory foam mattress but I (like your wife it seems) don’t believe they are good value. There are many high quality memory foams mattresses with better value IMO.
The most important first step in buying a mattress is to find one or a few outlets that have great value, a selection of choices using different materials, and that also knows how to fit you to a mattress. The more they know and are willing to guide you with their knowledge the less you have to know. The better outlets generally have no sales or at least only rarely and not for huge discounts.
The best choices are usually local factory direct outlets or smaller sleep shops that carry local brands. This is where you usually find the lowest profit margins, no fake sales, and the type of people who really do care about your long term satisfaction with their product. They will also tell you what is in each layer of a mattress, the quality of the layer, and why it is there. I would do some initial research on the phone and talk with them about what you are looking for and find out what they carry that would be suitable in your price range. I would then visit the ones that seemed most promising and helpful to test mattresses in person. With a knowledgeable person to guide you as you lie on mattresses, mattress shopping can be more enjoyable than frustrating.
I also wouldn’t get too caught up with all the “names” that are used for similar materials. Each manufacturer has their own name for memory foam and now each also has their own name for gel infused memory foams which are becoming quite popular mostly because of Serta’s advertising and promotion. I wouldn’t consider the iComfort to be a good value option (in the same way that the major brands are usually poor value) as the type of gel foam they use contains particles of gel which I believe will reduce the durability of the foam. The best gel memory foams actually have the gel as part of the foam itself rather than as added thin surface layers, inserts into holes in the memory foam, or particles in the foam. Is there a reason you are attracted to the Restonic TempaGel in particular? The licensees that manufacture Restonic have the choice of what they use in their mattress and Restonic is different in different areas of the country but at least in some areas of the country I know they are using the"swirl" gel meaning that it doesn’t have particles and would be a better “gel” choice.
So you have some great choices of outlets in your area and with a little bit of research on the phone and a few visits to the ones that impress you the most you should be able to find a great quality and value mattress within your budget.