I kind of wonder, Yoda and Obi-wan went poof when they died and became Force ghosts. Anakin didn't but became a Force ghost after cremation. Is there something where the physical body of a Force user has to be atomized/vaporized/turned to smoke before their Force ghost can roam free and until then they're stuck hanging out with their bodies?

The first person to say "a Force ghost is just a cloud of free-roaming midichlorians retaining a personality" is asking for a punch in the teeth, jsyk.