I can think of two solutions. Switch to a recumbent stationary bike, or do short, intense workouts where you alternate between sitting and standing. When you ride a conventional stationary bicycle, you sit on a narrow bicycle seat because your legs have to reach around the seat down to the pedals. The pudendal nerve in your pelvis can be pinched by the seat to cause numbness and pain in your crotch and genitals. When you sit on a recumbent bicycle that has the pedals at the same height as your pelvis, your legs are not separated by the seat so you don't need a narrow bicycle seat. You sit on a seat shaped like a regular chair which is contoured to fit your back and is very comfortable. Anyone who can sit in a chair can use a recumbent stationary bike, so even elderly people with poor coordination and weak muscles can get the benefits of exercise.
My current favorite workout bike is a "spinning" bike, the same kind used for classes in many gyms. It’s an upright bike with a standard narrow seat, but you don’t get sore because you never sit for long. In a "spinning" workout you cycle as fast and as hard as you can for brief periods, changing positions and resistance frequently. The bike has a very heavy wheel that moves smoothly and adjusts easily. In spinning classes, you have an upbeat instructor, music and other cyclists to keep you motivated, but you can do the same workout on your own. Used, reconditioned spinning bikes are available at reasonable prices if you decide you’d like to have one at home.