I was happy with My Mini Marvel https://uk.pcpartpicker.com/b/TYZRsY - but then quite quickly moved to the NZXT H200 case.
Then, after seeing the Louqe Ghost S1, I really wanted to try a truly SFF PC.
There were only two difficulties:
Sourcing a Ghost S1 in the UK - there's lots of delays currently, so in the end I found a second-hand one on eBay. The advantage was that it was completely new condition, and only £140. The disadvantage was that it was missing the front button cap, the internal kettle/IEC lead, and worst of all, the riser cable.
The GPU didn't quite fit - fortunately it was fairly easy to cut a little of the plastic fan shroud near the IO panel.