Hi lasdj,
Quilting over latex can certainly affect the feel of latex in several ways depending on the type of quilting and its thickness and the tightness of the quilt and the ticking.
In general, the softer the latex underneath, the more the quilt will affect its ability to conform to your body profile and relieve pressure.
If the quilt is made with fibers like wool or synthetic fibers, then as they compress, they can get firmer and also slightly interfere with the ability of the latex to compress and take on your body shape. This can cause some pressure issues over time in some while for others, it can help with alignment as they can benefit from sinking in slightly less.
They can also make a mattress with slightly firmer latex on top feel slightly softer and they (especially some soft polyfoam) give a āhand feelā (the feel of the top of the mattress when its pressed in a bit) and a ālookā that people are more used to.
In some mattresses ⦠the wool can also be used as a method of fire retardancy instead of other methods like a āsockā or various other ācompoundsā or chemicals which are added to fabric or foam to pass the fire regulations.
Finally, most fibers (especially natural ones) are quite breathable and can help to regulate sleeping temperature staying cooler in summer and warmer in winter. They are often added to a mattress or a mattress protector or pad for this reason.
All in all, it is a series of tradeoffs that can benefit some and detract for others. Either way they will certainly affect how the mattress as a whole performs.
If a mattress is finished without a zipper ticking ⦠then a quilting on top cannot be removed or exchanged and IMO ⦠any wool or other fiber that is added would be better added in the form of a mattress protector or pad as this would allow the protector or pad to be exchanged if necessary. If it has a zipper cover, then the cover can be exchanged if necessary. All of these āticking/quiltingā adjustments and choices can āfine tuneā the performance and feel of a mattress.
The āsafestā bet if you have tested mattresses with a certain layering without a quilt would be to add any wool as a mattress protector. The trend ⦠with good reason ⦠is towards latex mattresses with soft latex and a thick stretchy ticking material on top rather than other materials (such as wool or polyfoam quilting) which can affect the feel of the soft latex. Having said this ⦠as long as the quilting material is ātaken into accountā in terms of how it will affect a mattress, then it may still be a preference for some. Of course the choice of ticking/quilting materials can also affect the price of a mattress, not just its feel, as the ticking quilting is a significant part of the cost and the materials used in it vary widely in their cost.
If you have tested a mattress with a 3" comfort layer and it worked for pressure relief for your height/weight and sleeping position, then that āpoints toā that thickness being good for you. If you were to consider other options, then it too should have a similar thickness and ILD of comfort layer (or the other layers of the mattress should be adjusted to accommodate a thinner layer). The 8500 has a 1.5" comfort layer and so is a very different mattress and not really comparable to the one you are testing at Flexus. The 10000 (with a 3" comfort layer) and built with similar lower layers would be much more directly comparable in terms of its construction.
If you have tested a mattress correctly for pressure relief and alignment in real life ⦠this is far more accurate than the ātheoryā of an online purchase even with layer exchanges. While a DIY yourself mattress is a great way to construct a mattress when there is not something locally to actually test or that has good value, it can also be confusing if layers need to be exchanged in terms of deciding which layers to exchange and what should replace what. Even here ⦠local testing used as a blueprint is I believe very important.
My own mattress purchase for example was a āfinishedā mattress with the layers glued together that had no real possibility of a comfort exchange (because it would have involved very large shipping costs) but I had done enough testing to know for sure exactly how every layer of the mattress would interact with each other and with me and my DH. For most who may not be quite as certain as I was of how every layer and ticking/quilting choice would affect their mattress and how it worked for them, this would have involved a huge risk.
In general, I would always choose a high quality/value mattress that I have personally tested over a DIY choice if the value (based in materials used and mattress construction) was roughly similar (within say 20%). If the value of a DIY that was similar to what you were testing was significantly better ⦠then I would choose this as the ābestā option.
For those who do not have a factory direct manufacturer or other high value retail direct outlet close to them that is high quality/value, then an online purchase that can be adjusted through a layer exchange or through a complete mattress exchange at low cost would normally be the ābestā choice. This would normally involve using local mattresses as a blueprint for the initial choices of materials, layering, and construction from the online source.
If a layered mattress is put together in a ticking that āfitsā then the lack of gluing will not be an issue as latex doesnāt tend to shift in use unless the whole mattress is moved in which case itās easy to align again. Gluing layers together or not though can change the feel and interaction of the layers.
Feel free to keep any questions coming as they hopefully will not only help you but many others who are facing the same choices 
Phoenix