If you have access to a porcelain or marble sink the correct height, I suggest you try this solo performance (or get help for 'mutual')
I began to masturbate even before I knew what was going on or what it was called. When I met the girl who was to become my first wife, she was so eager for her first penetration sex that we never went through a mutual masturbation phase in our relationship.
We were married 2-1/2 years when she suddenly lost interest in sex. I had been gradually returning to solo masturbation. We had bought a house, and the bathroom was on the second floor. The window looked out on the driveway and only the top half was clear; the lower half was frosted. I had plenty of warning if she came home early. She couldn't surprise me and catch me masturbating in the bathroom.
I used to get home from work about 90 minutes before her. I would strip completely in the bedroom, then go into the bathroom naked and stroke myself off while standing in front of the mirror over the bathroom sink. I would cum into the sink, which made for easy cleanup.
One day the house was very cold and I stood unusually close to the sink. The marble rim touched both the underside of the base of my cock and my balls inside my scrotum. What a chill! What a turn-on! From then on, I always ensured that the cold marble rim was resting tightly up against my nut sack and the bottom of my shaft.
About two years later I had a mistress. She seldom came to the house; I usually went to her place, but each time she was at my house I would have her jack me off into that sink whilst my cock and balls were pressed up against the cold rim. At first, she rested her left hand in the crack of my ass while she stood naked behind me and at my right side and stroked me off with her right hand. Then one time she brought a lubricated condom, and she slipped it onto the two longest fingers of her left hand. While she was stroking me with her right hand, she knelt down on the floor and pressed her condom-covered fingers upward into my rectum. She curved her fingers toward the front of my body, pressing on my prostate. I came so hard that my first two cum spurts hit the mirror in front of my eyes. What an incredible orgasm!