Hey Martoof,
Yep looks like Blend Spaces aren't going to work for us.
I'm not a veteran or a dev by any means, but I did spend all day today on the same problem. Seems to me the easiest way to switch animations and get that nice smooth blend between bones, is these here nodes (attached). The Set Mix Duration node gives it that smooth blend.
NB. For some reason the Default Mix in the Spine Skeleton Data Asset, which is supposed to do that same smooth blend, doesnt work.