Hello ted3

Congratulations on being able to resume driving. Nothing gives as much of a boost to your sense of well-being like being able to return to everyday tasks and pleasures.
I, too, was looking for some protection for both the incision site as well as for the device itself while behind the wheel. And like you, I did not see anything that I thought would do the job on Amazon, etc.
However, I came upon a product, SoftTouch, that is purposely designed for pacemakers and ICDs. I bought two for myself and have recommended the product to many others. I have had my SoftTouch units for 3 years and, while not inexpensive, they are well made, sturdy and easy to use. The placement on the seat belt is adjustable and they are comfortable to wear. Plus they do provide protection for the unit itself in case you are involved in a collision. (A friend of mine was involved in a collision and his pacemaker was dislodged by the force of the seat belt.) They do provide both physical protection and some peace of mind.
The following is a description of the product:

"The patented SoftTouch™ seat belt pad is designed to provide comfort and a level of protection to patients with implanted devices or other medical conditions while wearing a seat belt.
Made with polyurethane and silicone gel and extensively tested at the Transportation Research Center, the unique design and construction of the SoftTouch pad enables the implanted medical device to sit in a free air space, reducing the forces over the region where the device is positioned, and better protecting the driver in the event of an automobile accident.
Discomfort can also occur due to seat belt vibration over the pacemaker implant area. SoftTouch lifts the shoulder belt, like a bridge, over the area of concern, eliminating direct contact between the medical device and shoulder belt while lessening vibration transmission."

And, although not applicable in your situation, they also make protectors for women's bras straps. Again, a really well designed product that is both durable (thinking of washing and drying) as well as unobtrusive to wear.
Further information about the products can be obtained at: information@AboutSoftTouch.com
Hope this information is of some use to you.
All the best.