Can someone recommend a plastic that I can mold?

I need a domed shape piece that is about 0.6-0.7 inch in height and width. The main problem is that I need the bottom to be rounded a bit. So I'm thinking of molding it.

If someone knows of a domed shape piece that I can sand the back to be a bit curved that'd be fine too. Basically, it'd look like a gumdrop and I'd add like to sand a curve into it.

Can anyone give me a recommendation?

Why don't you use fiberglass? Carve a piece of blue foam into the shape you like, make a mold from it, then fiberglass the mold. you'll have a perfectly fitting smooth piece to use for your purposes.

Ok, but it needs to be fairly durable. It'll have moderate pressure/bumping on it. Also, I need the bottom to be solid so I can superglue it.

This may be a stupid suggestion, but if it has to endure pressure and dumping, can't you use a (rubber) doorstop? At least as the basis, using a sharp knife and sanding paper to get it into the shape you want.

Actually, that is a good idea. Thank you for pointing that out to me.