Hi areginer,
I think you’ve clearly done some good research and your final choices seem to be between “good and good” although I don’t know the exact specs of the Easy Rest 14" gel memory foam mattress.
The foundation thread here has some of the better foundation options I’m aware of. I don’t know anything about the quality or construction details of the foundation you linked or the type or distance between the slats. I wouldn’t use it for a latex mattress (the gaps are too wide) but your mattress will have a polyfoam base and looking closely it seems to have 10 slats so if the slats were good quality, preferably 1x3, didn’t flex, and had good center support, it would probably be suitable.
I’m looking forward to finding out about your final choice … and of course your feedback when you receive it. I think that mattress shopping can be one of the more tiring things we do … and sleep always sounds good when it’s done 
Phoenix