I have found another way to have that 'full' feeling.
I use a normal 11" latex balloon.
First, I infalte it with air to stretch it out a little.
I tyhen put it over the bathroom sink tap, and put hot water in it and tie it off.
Depending on how horny I am, it can have up to 750ml in it. The sensation of inserting the hot water balloon inside can give me a nearly immeadiate orgasm.