I'm trying to learn this song on my soprano ukulele for my friend's wedding in a few months:

chords: https://tabs.ultimate-guitar.com/j/joanna_newsom/clam_crab_cockle_cowrie_crd.htm

audio: https://www.youtube.com/watch?v=F-xUpdO3g44

I am finger picking and it sounds right, but my problem is my thumb cramps up so much just in the first few lines. I am used to chords where the neck is making contact with my palm so my thumb is not doing anything. With these chords i have to press my thumb into the neck pretty hard to be able to pick each string and make a clear sound. I've heard the advice that I shouldn't press so hard, but if I don't then the sound is very muted. Any suggestions on different holds? any other possible solutions? Thanks so much!

Come over and we can practice holding each other.