Thank you all. Maybe the best way to describe this is to envision the profile of a cartoonish helium balloon. Oval, and fairly solid, bright-ish color (those 1.5mm thick carnelian pieces sound interesting). Probably 16x12mm to 18x13mm in size.
I have a design in mind (which I'll share here if it works, and probably won't if it doesn't) that I'd like to experiment with. If it does work, I'll want to take the design further.
Sometimes I just have to make something first to see if it stands up to the image in my head.