I honestly think the 950 is the smallest W10M phone that fits the bill. The 930 and 830 are also smaller Qi-equipped alternatives that also run W10M but they're older if that's an issue.
Also see the 735 which is even smaller (4.7") and officially supported for now. (with Qi as well)
Just left my 735 for something with more RAM/ROM. It was an absolute delight on 8.1. I'd be wary and check the forums about its performance on W10M, though... And IIRC, a Qi backplate had to be bought separately. Never had one myself but did see contacts for it "behind the curtain."
Love the size of that device though. Really wish I could find another 4.7" mid-ranger like the 735. The 950 (5") has definitely *just* gone over my comfort level.