I've got one of these https://www.asrock.com/mb/Intel/Q1900-ITX/ going spare if that suits - fully boxed with all accessories, never been used as it was a replacement for one i thought had blown but it was the pico power supply that failed so i moved enclosures to a corsair 250d and bunged in more hard drives and a silverstone psu - works perfect as my media machine and runs plex just fine - even to point of transcoding and streaming over internet for plex pass on my phone/tablet/friends tvs. £25 inc rm 2nd class postage.
Thanks for the very kind offer but the height of the heatsink and rear connectors is an issue, I need to go with Thin ITX. I am looking at something like the Jetway mentioned earlier or something like a B85TN motherboard I am watching on fleabay.