Go to your local music store and play guitars from differernt makers. For my hand the round neck of Fender guitars cramp me up quite fast. The flatter necks like Gibsons work pretty well. How wide a neck is can also make a hugh difference in how long you can play bar chords before the cramping starts. Use boxer clamps to strenthen your hands, slowly. The stronger your hand is the less pressure you have to apply to make the chords ring right.

Just play different guitars. Your left hand will tell you what it likes and can play without cramping.

It also seems guitars that cost less than $500.00 +/- seem to cramp my hand up way fastger than the $600.00 plus guitars do.

I've been playing for 35 years now.