I have been using short Gif as the base for the morph project, because they get to the interesting part of the scene and easier to load into after effect, however they tend to be blurry, so I try to find the biggest resolution gif first. If I cant, then I go to the mpg video. Sometimes the original old movies are better than the new wider screen version, because they cut off the bottom and top part of the screen. But lately there seems to be abundent of good resoluted gif animation to pick from.
I would expand the breast right half and left half into separate render pass and then mask each one back over the original clip. That works well for female that have some spaces between the breast, but for people like Wendy4 then sometime I just use one bulge effect over both breast at the same time.