Ball Joint

2.5mm Ball Joint
You might need to fiddle with infill and extrusion multiplier to get them to work and have your bed height just right, maybe a raft would be worth a try.
I go from what I use normally 0.96 to 0.9 on extrusion and 50% infill.
To break the ball free screw a 2.5mm bolt into the ball and wiggle it round. I usually get 4 out of 5 to work.

Also made a 3mm and 2mm, but haven't got the 2mm to work yet and you could just drill the 2.5mm one to 3mm and get a smaller joint.