One item I have not seen mentioned to simulate a vagina is a simple and wonderful ready-made product: a Hot/Cold pack. It's a plastic bag about 10 inches long and 4 inches wide by maybe 1/4" thick. It is usually filled with a blue gel. If you let it soak in hot water for a few minutes, it gets to body temperature. Then you can squeeze some lube all over your penis and wrap the "pack" around your erection. You can make a sleeve out of a sock or just use your hand to adjust tension. This pack makes a nice and easy humping or masturbation experience, and it's washable and reusable. I haven't investigated, but larger versions of these Hot/Cold packs may be available. That would make it nicer for those with Erecti giganticus.