A potato

You don't really want to put something alive in there. Another person is out of idea, and despite the fact that you find both your mom and sister quite a hot piece of ass, you don't think that being them is the right aim today. No. You want to fuck them with your own dick, not have masturbation session by putting them on and stroking your own dick with their hands.

Besides, you don't think you are ready to mess with having a pussy yet. Those tits your mom had were sensitive. You shove your videogame controller in your sister, but it doesn't really do anything. The seams don't seal up and the suit remains a suit.

Then an idea hits you. You go down to the kitchen and get a potato from the pantry, and stuff it in. I mean, it's still a plant. It's a living thing. Never had a brain once its life so probably won't even have a thought. And even if it does, would a plant even know how to operate a human body?

You stuff a potato in your mom. And it works. Suddenly you are staring at your mom staring blankly back at you. You grab her tits and squeeze, and she doesn't even react. You see her face blush as her heart beats faster, but it's just a natural reaction to arousal.

Booyah. Now you have your mom as a personal sex toy.