My wife and I decided to look for a new mattress because we seem to wake with more back pain each morning and wake up several times each night. We have an innerspring about 6 years old which appears fine but we believe does not support us properly. During research, I discovered Mattress Underground and have gained a lot of insight about mattresses. I think a latex might be best but have no experience with one. We live in the southern tip of Texas and opportunities to test a latex mattress locally are nil. However, we are taking a trip to California so we are going to stop in San Antonio, Phoenix and of course Southern CA at several mattress suppliers. I believe we will consider something similiar to 3" Talalay med/soft top, 3" med/firm middle and 3" firm/ex-firm botttom, perhaps split, bottom layer perhaps dunlop. We are 60 and 65 yrs, 130# & 185#, primarily side sleepers and seem to prefer a little firmer. I have phoned several suppliers who are more than willing to point out the shortcomings of competitors. If they glue the layers they explain they will bunch up if not glued; if they don’t, you can feel the glued seams, etc. I don’t know if we will feel the split if we decide on one of those or if we would be better off with a zoned and split; or 4 layers of latex instead of 3. I will certainly be back asking Pheonix about the claims we will be evaluating and will provide my perception of the places we visit (Foam Sweet Foam, AZ Mattress Co, SleepEZ, Flexus Comfort Beds, Optirest and Cantwell Mattress). Thanks to Mattress Underground for all the great info!
Hi TexMac,
That’s some kind of long distance mattress research! 
There is one factory direct manufacturer Furniture Row® Store Locations - Store Hours & Addresses which has two outlets in the area (Brownsville and Pharr) which makes two mostly latex mattresses (both have an inch of polyfoam in the upper layers which is OK) that may be worth including in your research (assuming they carry the latex models) before you start your travels.
Unglued layers are not an issue with shifting for the most part because latex is very “sticky” and will stay in place with a good ticking around it (unless you are moving the mattress or putting it on its side etc) so in those cases where shifting was an issue a zip cover makes it easy to re-align them.
Almost all talalay latex layers larger than twin XL have a glue seam (there are a few queen size molds but these are very uncommon) and many Dunlop layers will as well. You won’t feel these if they are glued correctly. They use (or should use) non toxic water based glue.
Post #2 here has some thoughts about split layering and how much it may be felt.
I’m sure looking forward to your feedback about your trip. You have some great choices included in your list.
Phoenix