Hi Jennamatty,
Welcome to the Mattress Forum! 
They are a “newer” brand that was introduced about a year ago (see here) offering latex mattresses using Talalay and continuous pour Dunlop latex. They’ve also started offering latex and memory foam mattresses and latex mattresses with springs as well. One of the partners (Kurt Ling) used to be one of the founders of Pure Latex Bliss which makes a range of latex mattresses. Both of the partners also worked with OMI which also makes a wide range of latex mattresses. The Posh + Lavish latex mattresses use high quality materials, but I would be cautious when considering them as part of your personal value equation, as there are other products available using similar materials at more reasonable prices.
There certainly can be large price variations when shopping for a mattress, which is why I would always make sure that you find out information listed here so you can compare the quality of the materials and components from mattress to mattress. There are many factors that are unique for each individual that go where you choose to purchase a mattress, and post #13 here has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you.
Sleep On Latex is a member of this site which means that I think very highly of them.
Latex, depending upon the type used (Talalay or Dunlop) and the combination of layers, can be helpful in minimizing motion transfer. Memory foam would be your best choice, followed by latex, and then followed by polyfoam. Also, consider your foundation and bed frame, making sure that they are solid and do not “amplify” your movement when in bed.
All foams, including latex, will contain come amount of chemicals, either in the final product or used up in the production process and rendered inert. The only reliable way to assess the “safety” of different materials in more general terms is based on lab tests and the certifications they have for harmful substances and VOCs (regardless of whether they are organic or natural or synthetic) so that you have some assurance than the VOCs are below the testing limits for the certification. If the materials in a mattress or the mattress itself has a reliable “safety” certification then for most people they would certainly be “safe enough” … regardless of the type of material or the name of the manufacturer on the label. All the latex you are likely to encounter (either Dunlop or Talalay that is made with either natural or synthetic rubber or a blend of both) will also have a reliable certification such as Oeko-Tex, Eco-Institut, Greenguard Gold or C2C and based on actual testing I would consider any type or blend of latex (regardless of whether it is synthetic, natural, or blended) to be a very “safe” material in terms of harmful substances and VOC’s (offgassing). You can read more about these safety certifications in post #2 here.
All foams are insulators to some extent, with memory foam being the most insulating, followed by polyfoam and latex. Talalay latex will generally be more breathable than Dunlop latex. Additionally, a softer mattress (one in which you sink in more deeply), will leave less of your surface area exposed for heat exchange, which can also have an effect on your sleeping temperature.
Overall, it’s not really possible to quantify the sleeping temperature of a mattress for any particular person with any real accuracy because there are so many variables involved including the type of mattress protector and the sheets and bedding that you use (which in many cases can have just as significant an effect on sleeping temperature as the type of foam in a mattress) and on where you are in the “oven to iceberg” range and because there is no standardized testing for temperature regulation with different combinations of materials … there is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range.
If you’re considering online latex options which may be more affordable for your particular application, I wouldn’t hesitate to use the experience and expertise of the members listed in post #21 here who are all very knowledgeable and specialize in providing the type of help and guidance on the phone that can help you make good choices. There are a wide range of latex options included in the choices there and I believe that all of them compete well with the best in the industry in terms of their quality, value, service, and transparency.
I’m looking forward to learning about your progress and if there are other questions that you may have.
Phoenix