There is a latex balloon on the market that is called a Geo. The balloon that I use to masturbate with is the 16' size Geo donut. This balloon has a hole in the middle that makes a fantastic substitute for a vagina.
I start out by pre-inflating the balloon to full capacity and then letting all the air out. When you re-inflate the balloon you will have a softer more squeezable balloon for a sex toy.
I lubricate the hole in the balloon and my cock with KY, do not use Vaseline as it will weaken the latex and cause the balloon to pop before you do!
I usually bounce the balloon up and down on my cock to make me cum, you can also use it standing up against a wall. The balloon hole is so tight, I usually cum really quickly.
The balloon can be cleaned up and re-used many times, I half knot the neck of the balloon to add more air later on if it starts to deflate.