Hi chloe41,
Hopefully this has been with careful and objective testing on mattresses where you are able to find out the specifics of the mattresses you tested that worked best for you in terms of PPP. If you are looking at an online choice then of course you would likely be looking at a different mattress design than what you tested (although you have hopefully tested the same materials) so your testing experience along with more detailed conversations with each online manufacturer you are considering would be the best way to choose which of the mattresses or options they offer would have the best chance of success (see mattress firmness/comfort levels in post #2 here).
Both of these are great choices and which one is best for you would depend on the parts of your personal value equation that are most important to you. Each person may be different. As you probably know from your research and conversations with each of them … one is a little lower final cost (after shipping is included) and the other has more options to customize, rearrange, and exchange layers after a purchase. Since both of these are great quality/value choices and there are no weak links or cautions with either of them, you are down to final choices between “good vs good” (see post #2 here) which is the place where only you can make the “best choice” for you (regardless of whether it may be the best choice for someone else).
Phoenix