Convexing is only marginally easier than working on stones. You still need to hold an angle properly, and you also need to have the right equipment and know how to use it.
Most folks start out with the old mousepad. If you are using something that soft, that is a problem. "Rock hard" felt is a terrific backing. Soft-ish leather works very well too.
There is still a learning curve. You won't be shaving anything at 400 grit until you are proficient with your equipment. It takes practice, just like anything else.