I know this isn't the most "store bought" thing but take your favorite dildo that has a wide base(one with balls would be best). Get an armless chair made of a material you think would feel good, probably leather of vinyl. Using shoelaces, tie the dildo to the chair at its base. Make sure to have the shoelace going from the dildo's base in all four directions and wrap around the chair's seat.
With this set up, sit down on the chair and enter the dildo into your vag, you should be able to side it pretty naturally if all goes well, and the best part is it will leave your bum fully exposed for him to enter