Take a small amount of olive oil and put it in a ziplock baggie - close it and smoosh the oil around until it coats the inside of the baggie. Open the baggie and fold the top of the baggie so the ziplock part is all on the outside.
Take a towel, fold a couple of times. Place the baggie in between the towel folds so the edge of the baggie sticks out a little.
Then take the whole thing and place it between a mattress and box spring. Then go for it. Pressing down on the mattress will change how 'tight' it feels.
It's a nice change from using hands.