Former Glock, former CZ, now SIG guy here.
See if you can find someone local with a SIG P320 and see how that shoots for you. They ship with a medium grip but since the entire grip swaps out its small grip is one of the smallest available on any double stack platform. The CZ could also be a good choice as long as you have no issues with trigger reach for the DA. Similar to what has been suggested you might also look at grip strengthening if the issue you are seeing isn't present at the beginning of a match. A steady dry fire routine should help greatly as well.