Hi Erianthe,
Most foam mattresses don’t have or need edge support but they will compress more if you put more concentrated weight on the outside few inches of the mattress compared to innerspring mattresses that have edge support (see post #2 here).
You can see my comments about Nest Bedding’s Love Bed and Brooklyn Bedding’s TheBestMattress ever along with some of the other “simplified choice” mattresses in post #2 in this topic.
There is also more about the difference between the “feel” of memory foam and latex in post #2 here. Both of the mattresses you are considering don’t have any memory foam so they will have a more resilient or springy “feel” than the Casper which uses memory foam underneath the latex.
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart who can help “talk you through” the specifics of their mattresses and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs or firmness options to different body types, sleeping positions, and preferences or even to other mattresses that they are familiar with than anyone else.
When you are down to finalists that are all choices between “good and good” (which you are) and none of them have any lower quality materials or “weak links” in their design (which they don’t) and if there are no clear winners between them then you are in the fortunate position that either of them would likely be a good choice and post #2 here can help you make a final choice based on your local testing or mattresses you have slept well on, your more detailed conversations with each of them, your confidence about PPP and the suitability of each one, their prices, your preferences, the options you have after a purchase to return or exchange the mattress, any additional extras that are part of each purchase, and on “informed best judgement” based on all the other objective, subjective, and intangible parts of your personal value equation that are most important to you.
Phoenix