Hi sarahnya,
While I can certainly help with “how” to choose … It’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress. There are just too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
There is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here 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 suitability, durability, and all the other 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).
I don’t see mattress called “medium” on the John Ryan site but if you can provide the information here about both mattresses and post the information on the forum I’d be happy to make some comments about them. There is also more information about the pros and cons of a wool quilted cover vs a more stretchy knit cover in post #6 here.
The choice between Talalay and Dunlop would be a preference and budget choice rather than a “better/worse” choice. There is more about some of the general differences between Talalay and Dunlop in post #7 here but the best way to know which type of latex you tend to prefer would be based on your own careful testing or your own personal experience.
If your slatted base is still in like new condition then if it’s suitable for one of them it would be suitable for both of them. The effect of adjustable slats will be less noticeable with a thicker latex mattress than it will for a thinner latex mattress.
Phoenix