I presently use an Asrock J5005 tdp 15W embedded motherboard in a low power build with a 30W Toshiba charger for my AC has a plug in dcdc z3-atx psu. Use the pcie 1x connector for an m.2 adapter, no gaming(Linux). Have used the Q1900DC, Q2900, J3710, this is fav so far. Probably be good for this use.
That's probly the way to go, I think... it's readyly available here in Brazil, it have a usable CPU (comparable in performance to the remarkable C2Q Q6600) and PCIe.
The only missing feature here to be considered perfect is the DC-Input.