Long term, a cucumber does it for me. Around 8 inches long, 1 to 2 inches in diameter, with a slight bend. As I insert it, the bend allows it to turn to adjust to the bend of the rectum/sigmoid connection. Cheap, plentiful, and innocent to the store clerk. If it goes in too far --- and that's the fun of it --- just bear down. The colon thinks it's just more fecal material. At least, that's been my experience. Just don't leave in too long. It may travel. LOL
I've recently seen in the better grocery stores a veggie called Chinese Egg Plant, or something similar. Purple-ish, 8-16 inches long, 1 1/2 inches long, and somewhat flexible.
And then there's the real Egg Plant, 2 1/2 to 4 inches in diameter (wow!).