Have you ever done the math about how much space your PC actually takes up? Lets take a totally average room, like maybe 16m². Lets assume 2m ceiling height, thats 32m³ of space. Now how large is the average midi tower? 0,25x0,5x0,6m? That works out to 0,075m³. Fairly small number compared to 32m³, isn't it. In fact the average midi tower works out to be 0,2% of the volume in an average room. Give or take.
Seems to me that fan is shit, or you're maybe using that PC as a pillow. If you went with a slightly larger case and a good passive solution, there wouldn't be any fans necessary.
I did that 15 years ago, when 120mm fans weren't a big thing. Case was made from wood, with foam for noise cancelling inside and labyrinths for the airflow. OC'ed AthlonXP that sucked way over 100W. Granted, not exactly SFF, but if silence is the priority, make it one.
Oh less TDP is nice to have, but its a rather low priority to me and realistically for most people its irrelevant. A few people obesess about it for no good reason, in my opinion. Lets say intel would sell 8Ghz Kaby Lakes with 1000W TDP, i would totally buy it.