Electric Radiant retrofit - what's best?

Looking at a 270 sf room with access below. House is all electric, so no hydronic option. Looking at 25 - 30 BTU per sf. Who has experience with electric, I'm assuming there's a spreader plate involved, the obvious radiant insulation, and controls. It will be one zone. There's decking (it's a sunroom), a subfloor, backer board and tile. Key will be to insulate underneath as part of it is exposed to the outdoors. I've done many hydronic systems and a few electric between the backer and the tile, but never one like this. Any help would be appreciated!
Matt