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Speaking as a climber.
Could go for chinese medicine balls (metal/stone)
Finger rolls https://stevenlow.org/finger-rolls-for-climbing-hand-strength-and-hangboard/
Also could consider using elastic bands (or even light theraband) which you likely already have where you can to extensor (wrap round fingers and spread apart) or contractor work (hold in other and and do curls).
Could look up the rice bucket method which I've never tried but some seem to rate for conditioning hands.
I broke my hand a while ago. Cast is now off and the Dr recommended some light exercises to physio my hand.
I’ve been looking at stress balls and they look fine but I was wondering if there’s anything not plastic available.