Hi katmack,
You can see my comments about a wire grid type of foundation in post #10 here. If the mattress you end up choosing has a latex support core like the Edsele then it may be worth adding a bed rug or a layer of firm polyfoam on top of the bedframe to lower the risk of the mattress compressing into the gaps in the wire grid surface over longer periods of time.
Polyfoam is stiffer and less flexible and “squishy” than latex so the risk would be less that along with the cover the polyfoam would sink into the gaps and the same bedframe would probably be fine.
Both Talalay and Dunlop (which is used in the Ikea) come in a range of firmness levels but Dunlop is denser than Talalay and gets firmer faster as you sink into it more deeply so in the same firmness level (ILD) the Dunlop would probably “feel” firmer to most people. Again this would only be true if the firmness level of both were the same. There is a little more about the difference in “feel” between them in post #7 here but the most reliable way to know which one you prefer is with your own testing or experience.
Once of the advantages of a local purchase is that you can do some careful and objective testing (using the testing guidelines) on the Edsele to make sure that it’s a good match for you in terms of PPP because it’s a “one size fits all” choice that may work well for some people but not for others. For many people it may be a little on the firm side because it doesn’t have separate comfort layers but personal testing or experience is the best way to know how suitable it may be for any particular person.
The advantage of the Ultimate Dreams is that you can choose the firmness of the comfort layer so you can have separate comfort layers for pressure relief and a firmer support core for support/alignment but I would also be aware that while it’s a great quality/value and customizable choice … it’s not one of their mattresses where you can exchange the comfort layer for a different firmness level after a purchase if it’s too firm or too soft for you so I would make sure that you have some more detailed conversations with them so they can help you choose the firmness level(s) that have the best odds of success based on “best efforts” and “averages”. If you are “stuck” in between two firmness choices that otherwise seem “equal” I would also lean towards the firmer one because you can always make a mattress that is too firm softer by adding a topper but it’s much more difficult to firm up a mattress that is too soft without removing and replacing the foam in either the comfort or support layers of the mattress.
A two sided mattress can extend the useful life of a mattress compared to a mattress that uses the same materials in a one sided version but this would only be a benefit if the mattress was a suitable choice in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) in the first place and as long as you flipped it on a regular basis.
Both of these would be good quality value choices so which one is “best” for you would depend on the parts of your personal value equation that were most important to you. You would be making a final choice between “good and good”.
Phoenix