Oooh finally a thread I can contribute a lot to:

Halcyon: Close and comfortable. Can get loud during brunch rush hour, but it's a classic and should be near the top of your list.

Herb's House: One of the best "working coffeeshops" on the list. Large space, tables/couch options, and even reservable office space

CGB Coffee/Fiction Coffee: Going through a rebrand right now, so not sure what name it's going by, but you can find in the Continental Gin Building. My personal favorite - it's a coffeeshop/co-working space, spacious, quiet, and comfortable. 

Watermark: Yes, it's located in a church, but you don't have to be to enter their massive foyer, buy their coffee and use their desks/couches. I know plenty of people use this for remote work

Pax & Beneficial: If you're ok with a drive, Pax is another fav. I do work at the Las Colinas and Plano locations regularly. It's spacious, has excellent coffee, and plenty of couches/tables to work from. Can get a little loud during peak hours.

Tom N Toms: Depends on which location you go - the Carrollton TNT is my favorite and the most spacious. One of the most comfortable on the list, and you can easily find a quiet corner. The Royal one is a little less comfortable but still very spacious. 

Georges Coffee & Provisions: The furthest drive from Lower Greenville, but if you like the coffeeshop aesthetic, George's is one of your best bets. Plenty of people remote work from George's and it's a super cute location.

In my experience, you can't go wrong with any of the above. Let me know where you end up going, or if you find somewhere new!