Hi handsoap,
You can see my thoughts about buying from Costco in post #4 here.
You can also see some comments about Sleep Science and the Escape in post #2 here and a forum search on Sleep Science Escape (you can just click the link) will bring up more comments and feedback about it as well (you can ignore the comments about not being CertiPUR certified since Southbay International which is the parent company of Sleep Science has been CertiPUR certified since the posts were written).
If you are comfortable with the additional uncertainty that goes with buying a mattress that is shipped compressed from China (see post#6 here and which may also account for some of the comments in the lower rated reviews about the mattress sagging) then if the mattress turns out to be a good match for you in terms of PPP (which of course you will find out once you sleep on it) then it is certainly a good quality/value choice.
Congratulations on your new mattress 
I’m looking forward to your comments and feedback once you’ve received it and have had the chance to sleep on it.
Phoenix