You may be able to benefit from a little exercise. I did, though not for writing. My grip strength had atrophied.
I found this el-cheapo machine working muscles deep into my palm as well as the fingers.
I write with heavy sterling pens. My ideas wear out before my hands do. Interestingly, I found that I have large differentials among fingers in strength. I also think it improved my coordination by forcing my fingers to act more independently, as in the picture. That hand model is going to get a powerful middle-finger if he keeps it up.
Simply hanging from a pull up bar or other tall object is far better at building up your grip compared to these little spring loaded gizmos.