Hi wimasoho,
Welcome to the Mattress Forum! 
If motion isolation is your primary concern, I would start your focus on the base that you are using, as it can be a source of motion transfer issues. You can see if you notice a difference by placing the mattress directly upon the floor and see if there is less motion transfer.
If you are considering a memory foam style of mattress, they can be excellent at motion transfer minimization. However, if such a mattress is placed upon a base that is not extremely solid and of a decent mass, you will still notice some motion transfer, regardless of the mattress.
When considering a new mattress, I can’t help with “what” to choose, but I certainly can provide guidance as to the “how” to choose. The first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which 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 (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
Outside of PPP (which is the most important part of “value”), the next most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t see or “feel” and assessing the durability and useful life of a mattress depends on knowing the specifics of its construction and the type and quality of the materials inside it regardless of the name of the manufacturer on the label or how a mattress feels in a showroom or when it is relatively new so I would always make sure that you find out the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
Tuft and Needle does not use memory foam in their mattresses – it is polyfoam.
I’d suggest you follow the guidelines I linked to above in selecting a mattress and avoid “reviews”. While other people’s comments about the knowledge and service of a particular business can certainly be very helpful … I would always keep in mind that you are the only one that can feel what you feel on a mattress and I would be cautious about using anyone else’s suggestions, experiences or reviews on a specific mattress (either positive or negative) or review sites in general as a reliable source of information or guidance about how you will feel on the same mattress or how suitable or how durable a mattress may be for you. In many if not most cases they can be more misleading than helpful because a mattress that would be a perfect choice for one person or even a larger group of people in terms of comfort, firmness, and PPP may be completely unsuitable for someone else to sleep on (even if they are in a similar weight range). In other words … reviews or other people’s experiences in general won’t tell you much if anything about the suitability, quality, durability, or “value” of a mattress for any particular person (see post #13 here).
While that will isolate each person’s movement from the other, I still think you may experience some of your own motion with the type of frame you are using.
I recommend following the guidelines linked to earlier in this post and focusing upon the componentry within a mattress. While having a good return policy might be an important part of your personal value equation, you’re better off starting with a mattress using higher quality componentry and then hopefully not have to take advantage of any potential return plan (most online companies offer return policies). If you’re considering looking online, you may wish to use the experience and expertise of the members listed in post #21 here who are all very experienced and 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 memory foam 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.
Hopefully this gives you a good starting point for your new search. If you have other questions after you’ve read through this material, I’ll be glad to do my best to be assistive.
Phoenix