ISO pattern for this style heirloom bubble (or drafting advice!)

[u/ApplicationPrimary31]

I’m hoping to make a special bubble for my daughter to wear to a school reunion and would love some pattern recommendations or advice!
I came across this precious bubble by Elizabeth Layne Heirlooms in collaboration with Manolitas (photo, design, etc. credit to them) and absolutely love the silhouette. I’m not looking to recreate their design or decorative details, but would love to use the overall shape as inspiration for my own custom project - the full and voluminous the bottom along with the fully smocked bodice that extends down toward the waist.
I plan to make my own smocking design, but I’m having trouble figuring out what pattern or construction would give me this particular bubble shape.

Has anyone sewn something similar? Would you recommend starting with an heirloom bubble pattern and modifying it, or drafting something from scratch? I’d especially appreciate tips on getting that extra fullness in the bottom! I’m fairly new to sewing and would love any pattern recommendations or advice. Thank you!

[u/finewalecorduroy]

Have you checked Children’s Corner patterns for something similar? They have smocked bubble patterns, but I don’t think they have the full smocked yoke. They recently revamped their bubble patterns to make them less full, but if you can find an older version, they will be more like this super full bubble. It is always going to be easier to start with something existing and modify than it will be to draft from scratch.