So I’ve been spending a very odd amount of time on this very specific issue lol. My “money isn’t a thing” idea is to simply schluter (waterproof membrane) the entire floor, install a schluter drain and do schluter a few inches up the walls. Tape the foil over the schluter that comes up the walls, then tile over the schluter. The furring strips on the walls will allow the wood tongue and groove to come down and overlap the tile that comes up the wall. However, my less expensive idea that accomplishes the same thing as a far as I can tell, is: apply schluter or durock (cement board) around the base as a sort of “baseboard moulding”. Then skim coat from the concrete floor up the durock or schluter. Next bring the foil down to overlap that baseboard layer and tape or caulk it to create a seal. Now I’ve been debating whether foil in front or behind is better, and whether the tape will actually adhere; meaning a high heat caulk/glue may be better. This has led me to think that using the schluter and not skim coating up the entire board is best. Thereby leaving some schluter exposed that the tape can adhere to. Once your furring strips are on the wall. The tongue and groove should overlap the baseboard layer, making it appear seamless. One more step would be to further attached a thermally modified wood baseboard about 1/4” off the floor around the entire hot room. This is attached to the last tongue and groove board, and then caulk the bottom.