Not having big luck with girls, I devised this technique. Maybe you know already, but anyway. You need a large bed with two mattresses, not a king size mattress.
Get a condom.
Place a sheet so that it lies smooth on the bed, taking care to leave some of it between the mattresses; how much depends on your cock size, in doubt, more is better.
Begin all sort of arousing thoughts. I find everything works definitely better if I start masturbating when I am already fully erect, instead than bringing myself to a hard-on with my hands.
Wear the condom. Now insert your penis between the mattresses, and hump away.
You may like to place a pillow under yourself, at the level where you belly is.
I've had plenty of satisfaction with this method.