You’re probably fortunate that you got 6 years from your mattress and I would think that your lower weight worked in your favor here. While I don’t know the exact specs of the Positano … it does seem to one of their upper end and very plush mattresses which means that it would also have had a great deal of lower quality polyfoam in the comfort layers.
I would tend to avoid polyfoam at all in the comfort layer (more than 1") unless you are at the lower end of the budget range and even here I would only include it if I was purchasing from a local manufacturer who could tell me the density and quality of the polyfoam they are using and how long it can reasonably be expected to last. It would be exceptionally rare to see a mattress with true HR polyfoam in the comfort layer, even from a local manufacturer … although you may see many places claiming they use it (without providing the specs). If you are looking at foam in your comfort layers (rather than natural fibers or other comfort materials that are described here) … your choice would be between latex and memory foam if at all possible. Some of the pros and cons of each are here (latex) and here (memory foam). If you know you like memory foam and have slept on it enough to know that you prefer this … then I would include it in your research. If you are not familiar with memory foam … then I would stick with latex as it is closer to the polyfoam feel you are used to … except it is a much higher quality foam but with better pressure relief, motion isolation, and durability qualities. Unless you are familiar with the feel of various foam combinations in your comfort layers … I would also tend to stick with one main material just for the sake of simplicity.
Lighter weights usually do best with softer foam on the top layers as they won’t sink into the mattress as much. Back sleeping is usually in the range of 2" in the comfort layer while stomach sleeping usually does best with the thinnest firmest layer possible (because of the tendency of stomach sleepers to “hammock” as their hips sink in and the back is hyperextended). A pillow under the hips and lower abdomen can help with this.
Some of the local factory direct manufacturers that are reasonably near either Philadelphia, or Wilmington, DE (within about 60 miles of any of them) include …
magicsleeper.net/ or http://www.mattressandfurniturestore.com/ Pottstown (or Pottsdown), PA. Local factory direct manufacturer that makes a range of good quality and value mattresses including two sided innerspring mattresses and a number of latex and latex hybrid options. They are family owned and good people. They also make custom designs and sizes and and they are also a member of this site.
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http://www.shovlinmattress.com/ Fanwood, NJ. Factory direct manufacturer. Very helpful and knowledgeable and a member of this site as well. Makes a range of mattresses using various high quality materials including latex, innersprings, and custom foam designs. Family owned and Ron Shovlin the owner is “mattress people” and also well worth a visit for those that are in reasonable driving range.
sichelsleep.com/index.html Norristown, PA. They have been making mattresses for over 100 years and make a range of two sided mattresses including latex, innersprings, memory foam, and still make old style tufted innerspring and cotton mattresses. I spoke with Red the owner here for several hours and he is knowledgeable and experienced and is fully transparent about the mattresses they make. Would also be well worth a visit.
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Directory of Verlo Mattress Locations. Find a Verlo Mattress store in your town. West Chester, Broomall, PA. Regional factory direct manufacturer with a wide range of mattresses using a range of all different materials. Have a good selection of mattresses.
https://www.mycustombedding.com/ Clark, NJ. Factory direct manufacturer that also hand builds a variety of mattresses using high quality materials including latex and horsehair.
http://www.croydonmattress.com/ Bensalem, PA. Local factory direct manufacturer who makes a range of mattresses. They are not as focused on information about their materials as other manufacturers and I had some difficulty getting answers to some of my more specific questions that were answered with generalities. Family owned and good people with reasonable but not the best value and transparency compared to many independent manufacturers. Make sure you find out the specs of the layers if you shop here as they may not be as willing as most manufacturers to disclose them.
https://www.whitelotushome.com/ Highland Park, NJ. Local factory direct manufacturer that focuses on mattresses using organic materials. Good quality but in a higher budget range than many local manufacturers.
Shop Affordable Home Furnishings & Home Goods - IKEA Philadelphia, Conshohocken, PA. Carries an all Dunlop latex mattress and other latex options. See post #3 here.
There are a wide range of styles, quality ranges, degrees of hand manufacturing, materials, and prices among these so I would look at their sites and call them first to do some “phone research” and let them know your specs, your preferences, and your budget range and see which ones seem closest to what you are looking for and which ones you “connect with” in terms of their helpfulness. Some of these will also build a side by side split so that each of you can tailor your side to your own needs and preferences.
There are also some retail outlets in the Philadelphia, Trenton, and Wilmington area (NOTE: updated since the original reply) that are worth mentioning. I would check their websites or call them first and go there if I was nearby or if you want to test different types of layering as a model for an online purchase or if a phone call or their website indicated they had a mattress that had particularly good quality and value. I have included some comments or at least the brands I would include in my research at each of them (ignoring any mainstream brands they may also carry) but most of these will require more research to find out know knowledgeable and transparent they are about the layers in their mattresses and the specifics of the mattresses they carry.
http://www.yourorganicbedroom.com/ Doylestown, Paoli, PA. Retailer that carries a range of high quality mattresses including OMI, WJ Southard, Naturepedic, Savvy Rest, SleepTek, White Lotus, and Suite Sleep mattresses. The Savvy Rest is a “choose your own layer” mattress that would be particularly valuable in testing latex layer combinations if you are considering an online purchase even though most of these are more premium mattresses and I would make sure you make some careful value comparisons.
https://theeastcoastorganicmattressstore.com/about/contact/ Hellertown, PA. They carry Suite sleep, GreenSleep, WJ southard, Naturepedic, and their own private label. These are all high quality mattresses and they have many latex options but they are also in more premium price ranges so I would make some careful value comparisons here as well.
https://www.shopgreendesign.com/ Retailer in Philadelphia, PA and Princeton, NJ that also sells Savvy Rest latex mattresses.
https://www.homemattresscenter.com/ in Wilmington, New Castle, and Newark, DE. They carry Ditex and Eclipse mattresses which may be worth considering here (I would avoid the major brands they carry).
https://www.chiromatic.com/ North Brunswick, NJ. Feasterville, PA. Local retailer. They work primarily through appointment and through chiropractor or medical referral and will fit the mattress to the needs of their customer and their chiropractors recommendations. Private appointments often mean “expensive” and IMO they fit this category by charging (or including an extra profit in their mattresses) for “fitting” that other manufacturers do as part of their regular service but they are listed for reference and may be worth a visit.
https://www.modernagefurniturephila.com/ Philadelphia, PA Therapedic, Eclipse, Ditex
https://www.eroomservice.com/ Philadelphia, PA. Magniflex (they may not be able to supply the specs in which case I would avoid them as I would with any retailer who can’t provide the specific information about all the layers of their mattresses)
https://www.brandywinefurniture.com/ Wilmington, DE. Symbol.
https://furnitureurban.com/ New Castle, DE. Eclipse, Therapedic
https://www.themattressfactoryinc.com/ Springfield, PA. and many others in the area. Therapedic, Eclipse
http://www.themattressmanonline.com/ Philadelphia, PA. Symbol (incl gel)
http://www.filachecksfurniture.com/ West Grove, PA. Englander
This should give you some good choices in your area both for high quality and value mattresses and some great advice in terms of finding a mattress that would suit your needs and preferences … and staying away from the lower quality and durability mattresses and foams that are so common in the chain stores and the major brands they sell.